diff --git a/rsconcept/frontend/src/context/LibraryContext.tsx b/rsconcept/frontend/src/context/LibraryContext.tsx
index 522744ad..8a2b719b 100644
--- a/rsconcept/frontend/src/context/LibraryContext.tsx
+++ b/rsconcept/frontend/src/context/LibraryContext.tsx
@@ -1,8 +1,8 @@
 import { createContext, useCallback, useContext, useEffect, useState } from 'react';
 
 import { ErrorInfo } from '../components/BackendError';
-import { matchLibraryItem } from '../models/library';
 import { ILibraryItem } from '../models/library';
+import { matchLibraryItem } from '../models/libraryAPI';
 import { ILibraryFilter } from '../models/miscelanious';
 import { IRSForm, IRSFormCreateData, IRSFormData } from '../models/rsform';
 import { loadRSFormData } from '../models/rsformAPI';
@@ -68,7 +68,7 @@ export const LibraryState = ({ children }: LibraryStateProps) => {
       result = result.filter(item => user?.subscriptions.includes(item.id) || item.owner === user?.id);
     }
     if (params.query) {
-      result = result.filter(item => matchLibraryItem(params.query!, item));
+      result = result.filter(item => matchLibraryItem(item, params.query!));
     }
     return result;
   }, [items, user]);
diff --git a/rsconcept/frontend/src/main.tsx b/rsconcept/frontend/src/main.tsx
index 11e57ed0..6f548cfe 100644
--- a/rsconcept/frontend/src/main.tsx
+++ b/rsconcept/frontend/src/main.tsx
@@ -44,5 +44,5 @@ createRoot(document.getElementById('root')!).render(
   </ThemeState>
   </IntlProvider>
   </ErrorBoundary>
-  </React.StrictMode>,
+  </React.StrictMode>
 )
diff --git a/rsconcept/frontend/src/models/language.ts b/rsconcept/frontend/src/models/language.ts
index 61890b60..ba4f0dae 100644
--- a/rsconcept/frontend/src/models/language.ts
+++ b/rsconcept/frontend/src/models/language.ts
@@ -260,6 +260,7 @@ export interface ISyntacticReference {
   nominal: string
 }
 
+
 /**
  * Represents text 0-indexed position inside another text.
 */
diff --git a/rsconcept/frontend/src/models/library.ts b/rsconcept/frontend/src/models/library.ts
index 3cd6684e..caa08629 100644
--- a/rsconcept/frontend/src/models/library.ts
+++ b/rsconcept/frontend/src/models/library.ts
@@ -1,8 +1,11 @@
-// Module: Schema library models.
+/**
+ * Module: Models for Library entities and Users.
+ */
 
-import { TextMatcher } from '../utils/utils'
-
-// ========= Users ===========
+/**
+ * Represents user detailed information.
+ * Some information should only be accesible to authorized users
+*/
 export interface IUser {
   id: number | null
   username: string
@@ -11,31 +14,63 @@ export interface IUser {
   first_name: string
   last_name: string
 }
+
+/**
+ * Represents CurrentUser information.
+*/
 export interface ICurrentUser extends Pick<IUser, 'id' | 'username' | 'is_staff'> {
   subscriptions: number[]
 }
+
+/**
+ * Represents login data, used to authentificate users.
+*/
 export interface IUserLoginData extends Pick<IUser, 'username'> {
   password: string
 }
+
+/**
+ * Represents signup data, used to create new users.
+*/
 export interface IUserSignupData extends Omit<IUser, 'is_staff' | 'id'> {
   password: string
   password2: string
 }
+
+/**
+ * Represents user data, intended to update user profile in persistent storage.
+*/
 export interface IUserUpdateData extends Omit<IUser, 'is_staff' | 'id'> { }
 
+/**
+ * Represents user profile for viewing and editing {@link IUser}.
+*/
 export interface IUserProfile extends Omit<IUser, 'is_staff'> { }
+
+/**
+ * Represents user reference information.
+*/
 export interface IUserInfo extends Omit<IUserProfile, 'email'> { }
+
+/**
+ * Represents data needed to update password for current user.
+*/
 export interface IUserUpdatePassword {
   old_password: string
   new_password: string
 }
 
-// ========== LibraryItem ============
+/**
+ * Represents type of library items.
+*/
 export enum LibraryItemType {
   RSFORM = 'rsform',
   OPERATIONS_SCHEMA = 'oss'
 }
 
+/**
+ * Represents library item common data typical for all item types.
+*/
 export interface ILibraryItem {
   id: number
   item_type: LibraryItemType
@@ -49,13 +84,9 @@ export interface ILibraryItem {
   owner: number | null
 }
 
+/**
+ * Represents update data for editing {@link ILibraryItem}.
+*/
 export interface ILibraryUpdateData
   extends Omit<ILibraryItem, 'time_create' | 'time_update' | 'id' | 'owner'> {
-}
-
-// ============= API ===============
-export function matchLibraryItem(query: string, target: ILibraryItem): boolean {
-  const matcher = new TextMatcher(query);
-  return matcher.test(target.alias) || matcher.test(target.title);
-}
-
+}
\ No newline at end of file
diff --git a/rsconcept/frontend/src/models/libraryAPI.ts b/rsconcept/frontend/src/models/libraryAPI.ts
new file mode 100644
index 00000000..cc25ce21
--- /dev/null
+++ b/rsconcept/frontend/src/models/libraryAPI.ts
@@ -0,0 +1,18 @@
+/**
+ * Module: API for Library entities and Users.
+ */
+
+import { TextMatcher } from '../utils/utils';
+import { ILibraryItem } from './library';
+
+/**
+ * Checks if a given target {@link ILibraryItem} matches the specified query.
+ * 
+ * @param target - item to be matched
+ * @param query - text to be found in target attributes
+ */
+export function matchLibraryItem(target: ILibraryItem, query: string): boolean {
+  const matcher = new TextMatcher(query);
+  return matcher.test(target.alias) || matcher.test(target.title);
+}
+
diff --git a/rsconcept/frontend/src/models/miscelanious.ts b/rsconcept/frontend/src/models/miscelanious.ts
index a2d668d6..0fd08b09 100644
--- a/rsconcept/frontend/src/models/miscelanious.ts
+++ b/rsconcept/frontend/src/models/miscelanious.ts
@@ -1,6 +1,6 @@
-// Module: Miscellanious frontend model types.
-
-import { IConstituenta, IRSForm } from './rsform'
+/**
+ * Module: Miscellanious frontend model types. Future tagets for refactoring aimed at extracting modules.
+ */
 
 /**
  * Represents graph dependency mode.
@@ -84,23 +84,3 @@ export interface GraphEditorParams {
   allowConstant: boolean
   allowTheorem: boolean
 }
-
-// ================== API ====================
-export function applyGraphFilter(schema: IRSForm, start: number, mode: DependencyMode): IConstituenta[] {
-  if (mode === DependencyMode.ALL) {
-    return schema.items
-  }
-  let ids: number[] | undefined = undefined
-  switch (mode) {
-    case DependencyMode.OUTPUTS: { ids = schema.graph.nodes.get(start)?.outputs; break} 
-    case DependencyMode.INPUTS: { ids = schema.graph.nodes.get(start)?.inputs; break} 
-    case DependencyMode.EXPAND_OUTPUTS: { ids = schema.graph.expandOutputs([start]); break} 
-    case DependencyMode.EXPAND_INPUTS: { ids = schema.graph.expandInputs([start]); break} 
-  }
-  if (!ids) {
-    return schema.items
-  } else {
-    return schema.items.filter(cst => ids!.find(id => id === cst.id))
-  }
-}
-
diff --git a/rsconcept/frontend/src/models/miscelaniousAPI.ts b/rsconcept/frontend/src/models/miscelaniousAPI.ts
new file mode 100644
index 00000000..40e35ab4
--- /dev/null
+++ b/rsconcept/frontend/src/models/miscelaniousAPI.ts
@@ -0,0 +1,29 @@
+/**
+ * Module: API for miscellanious frontend model types. Future tagets for refactoring aimed at extracting modules.
+ */
+
+import { DependencyMode } from './miscelanious';
+import { IConstituenta, IRSForm } from './rsform';
+
+
+/**
+ * Filter list of  {@link ILibraryItem} to a given query.
+ */
+export function applyGraphFilter(target: IRSForm, start: number, mode: DependencyMode): IConstituenta[] {
+  if (mode === DependencyMode.ALL) {
+    return target.items
+  }
+  let ids: number[] | undefined = undefined
+  switch (mode) {
+    case DependencyMode.OUTPUTS: { ids = target.graph.nodes.get(start)?.outputs; break} 
+    case DependencyMode.INPUTS: { ids = target.graph.nodes.get(start)?.inputs; break} 
+    case DependencyMode.EXPAND_OUTPUTS: { ids = target.graph.expandOutputs([start]); break} 
+    case DependencyMode.EXPAND_INPUTS: { ids = target.graph.expandInputs([start]); break} 
+  }
+  if (!ids) {
+    return target.items
+  } else {
+    return target.items.filter(cst => ids!.find(id => id === cst.id))
+  }
+}
+
diff --git a/rsconcept/frontend/src/models/rsform.ts b/rsconcept/frontend/src/models/rsform.ts
index 955bb627..ca3fb1f4 100644
--- a/rsconcept/frontend/src/models/rsform.ts
+++ b/rsconcept/frontend/src/models/rsform.ts
@@ -1,8 +1,15 @@
+/**
+ * Module: Models for formal representation for systems of concepts.
+ */
+
 import { Graph } from '../utils/Graph'
 import { ILibraryUpdateData } from './library'
 import { ILibraryItem } from './library'
 import { IArgumentInfo, ParsingStatus, ValueClass } from './rslang'
 
+/**
+ * Represents Constituenta type.
+*/
 export enum CstType {
   BASE = 'basic',
   STRUCTURED = 'structure',
@@ -17,6 +24,9 @@ export enum CstType {
 // CstType constant for category dividers in TemplateSchemas. TODO: create separate sctructure for templates
 export const CATEGORY_CST_TYPE = CstType.THEOREM;
 
+/**
+ * Represents Constituenta classification in terms of system of concepts.
+*/
 export enum CstClass {
   BASIC = 'basic',
   DERIVED = 'derived',
@@ -24,7 +34,9 @@ export enum CstClass {
   TEMPLATE = 'template'
 }
 
-// Constituenta expression status
+/**
+ * Represents formal expression Status.
+*/
 export enum ExpressionStatus {
   VERIFIED = 'verified',
   INCORRECT = 'incorrect',
@@ -34,12 +46,17 @@ export enum ExpressionStatus {
   UNKNOWN = 'unknown',
 }
 
+/**
+ * Represents word form for natural languange.
+*/
 export interface TermForm {
   text: string
   tags: string
 }
 
-// ====== Constituenta ==========
+/**
+ * Represents Constituenta basic persistent data.
+*/
 export interface IConstituentaMeta {
   id: number
   schema: number
@@ -55,6 +72,9 @@ export interface IConstituentaMeta {
   term_forms: TermForm[]
 }
 
+/**
+ * Represents Constituenta.
+*/
 export interface IConstituenta
 extends IConstituentaMeta {
   cst_class: CstClass
@@ -69,10 +89,16 @@ extends IConstituentaMeta {
   }
 }
 
+/**
+ * Represents Constituenta list.
+*/
 export interface IConstituentaList {
   items: number[]
 }
 
+/**
+ * Represents constituenta data, used in creation process.
+*/
 export interface ICstCreateData 
 extends Pick<
   IConstituentaMeta, 
@@ -82,23 +108,37 @@ extends Pick<
   insert_after: number | null
 }
 
+/**
+ * Represents data, used in ordering constituents in a list.
+*/
 export interface ICstMovetoData extends IConstituentaList {
   move_to: number
 }
 
+/**
+ * Represents data, used in updating persistent attributes in {@link IConstituenta}.
+*/
 export interface ICstUpdateData
 extends Pick<IConstituentaMeta, 'id'>,
 Partial<Pick<IConstituentaMeta, | 'alias' | 'convention' | 'definition_formal' | 'definition_raw' | 'term_raw' | 'term_forms'>> {}
 
+/**
+ * Represents data, used in renaming {@link IConstituenta}.
+*/
 export interface ICstRenameData 
 extends Pick<IConstituentaMeta, 'id' | 'alias' | 'cst_type' > {}
 
+/**
+ * Represents data response when creating {@link IConstituenta}.
+*/
 export interface ICstCreatedResponse {
   new_cst: IConstituentaMeta
   schema: IRSFormData
 }
 
-// ========== RSForm ============
+/**
+ * Represents {@link IRSForm} statistics.
+*/
 export interface IRSFormStats {
   count_all: number
   count_errors: number
@@ -119,6 +159,9 @@ export interface IRSFormStats {
   count_theorem: number
 }
 
+/**
+ * Represents formal explication for set of concepts.
+*/
 export interface IRSForm
 extends ILibraryItem {
   items: IConstituenta[]
@@ -127,14 +170,23 @@ extends ILibraryItem {
   subscribers: number[]
 }
 
+/**
+ * Represents data for {@link IRSForm} provided by backend.
+*/
 export interface IRSFormData extends Omit<IRSForm, 'stats' | 'graph'> {}
 
+/**
+ * Represents data, used for creating {@link IRSForm}.
+*/
 export interface IRSFormCreateData
 extends ILibraryUpdateData {
   file?: File
   fileName?: string
 }
 
+/**
+ * Represents data, used for uploading {@link IRSForm} as file.
+*/
 export interface IRSFormUploadData {
   load_metadata: boolean
   file: File
diff --git a/rsconcept/frontend/src/models/rsformAPI.ts b/rsconcept/frontend/src/models/rsformAPI.ts
index c412cd64..eab19bd0 100644
--- a/rsconcept/frontend/src/models/rsformAPI.ts
+++ b/rsconcept/frontend/src/models/rsformAPI.ts
@@ -1,4 +1,7 @@
-// ========== RSForm API =================
+/**
+ * Module: API for formal representation for systems of concepts.
+ */
+
 import { Graph } from '../utils/Graph';
 import { TextMatcher } from '../utils/utils';
 import { CstMatchMode } from './miscelanious';
@@ -9,8 +12,15 @@ import {
 import { ParsingStatus, ValueClass } from './rslang';
 import { extractGlobals } from './rslangAPI';
 
-export function loadRSFormData(schema: IRSFormData): IRSForm {
-  const result = schema as IRSForm
+/**
+ * Loads data into an {@link IRSForm} based on {@link IRSFormData}.
+ *
+ * @remarks
+ * This function processes the provided input, initializes the IRSForm, and calculates statistics
+ * based on the loaded data. It also establishes dependencies between concepts in the graph.
+ */
+export function loadRSFormData(input: IRSFormData): IRSForm {
+  const result = input as IRSForm
   result.graph = new Graph;
   if (!result.items) {
     result.stats = {
@@ -75,7 +85,7 @@ export function loadRSFormData(schema: IRSFormData): IRSForm {
     result.graph.addNode(cst.id);
     const dependencies = extractGlobals(cst.definition_formal);
     dependencies.forEach(value => {
-      const source = schema.items.find(cst => cst.alias === value)
+      const source = input.items.find(cst => cst.alias === value)
       if (source) {
         result.graph.addEdge(source.id, cst.id);
       }
@@ -84,6 +94,13 @@ export function loadRSFormData(schema: IRSFormData): IRSForm {
   return result;
 }
 
+/**
+ * Checks if a given target {@link IConstituenta} matches the specified query using the provided matching mode.
+ *
+ * @param target - The target object to be matched.
+ * @param query - The query string used for matching.
+ * @param mode - The matching mode to determine which properties to include in the matching process.
+ */
 export function matchConstituenta(target: IConstituenta, query: string, mode: CstMatchMode): boolean {
   const matcher = new TextMatcher(query);
   if ((mode === CstMatchMode.ALL || mode === CstMatchMode.NAME) && 
@@ -104,6 +121,20 @@ export function matchConstituenta(target: IConstituenta, query: string, mode: Cs
   return false;
 }
 
+/**
+ * Infers the status of an expression based on parsing and value information.
+ *
+ * @param parse - parsing status of the expression.
+ * @param value - value class of the expression.
+ * 
+ * @returns The inferred expression status:
+ * - `ExpressionStatus.UNDEFINED` if either parsing or value is not provided.
+ * - `ExpressionStatus.UNKNOWN` if parsing status is `ParsingStatus.UNDEF`.
+ * - `ExpressionStatus.INCORRECT` if parsing status is `ParsingStatus.INCORRECT`.
+ * - `ExpressionStatus.INCALCULABLE` if value is `ValueClass.INVALID`.
+ * - `ExpressionStatus.PROPERTY` if value is `ValueClass.PROPERTY`.
+ * - `ExpressionStatus.VERIFIED` if both parsing and value are valid.
+ */
 export function inferStatus(parse?: ParsingStatus, value?: ValueClass): ExpressionStatus {
   if (!parse || !value) {
     return ExpressionStatus.UNDEFINED;
@@ -123,11 +154,26 @@ export function inferStatus(parse?: ParsingStatus, value?: ValueClass): Expressi
   return ExpressionStatus.VERIFIED;
 }
 
+/**
+ * Checks if given expression is a template.
+ */
 export function inferTemplate(expression: string): boolean {
   const match = expression.match(/R\d+/g);
   return (match && match?.length > 0) ?? false;
 }
 
+/**
+ * Infers the {@link CstClass} based on the provided {@link CstType} and template status.
+ *
+ * @param type - The CstType representing the type of the Constituenta.
+ * @param isTemplate - A boolean indicating whether the Constituenta is a template.
+ *
+ * @returns The inferred CstClass based on the combination of CstType and template status:
+ * - `CstClass.TEMPLATE` if the Constituenta is a template.
+ * - `CstClass.BASIC` if the CstType is BASE, CONSTANT, or STRUCTURED.
+ * - `CstClass.DERIVED` if the CstType is TERM, FUNCTION, or PREDICATE.
+ * - `CstClass.STATEMENT` if the CstType is AXIOM or THEOREM.
+ */
 export function inferClass(type: CstType, isTemplate: boolean): CstClass {
   if (isTemplate) {
     return CstClass.TEMPLATE;
@@ -144,11 +190,16 @@ export function inferClass(type: CstType, isTemplate: boolean): CstClass {
   }
 }
 
-export function isMockCst(cst: IConstituenta) {
-  return cst.id <= 0;
-}
-
-export function createMockConstituenta(schema: number, id: number, alias: string, type: CstType, comment: string): IConstituenta {
+/**
+ * Creates a mock {@link IConstituenta} object with the provided parameters and default values for other properties.
+ */
+export function createMockConstituenta(
+  schema: number,
+  id: number,
+  alias: string,
+  type: CstType,
+  comment: string
+): IConstituenta {
   return {
     id: id,
     order: -1,
@@ -175,16 +226,26 @@ export function createMockConstituenta(schema: number, id: number, alias: string
   };
 }
 
-export function applyFilterCategory(target: IConstituenta, schema: IRSFormData): IConstituenta[] {
+/**
+ * Checks if given {@link IConstituenta} is mock.
+ */
+export function isMockCst(cst: IConstituenta) {
+  return cst.id <= 0;
+}
+
+/**
+ * TODO: description
+ */
+export function applyFilterCategory(start: IConstituenta, schema: IRSFormData): IConstituenta[] {
   const nextCategory = schema.items.find(
     cst => (
-      cst.order > target.order &&
+      cst.order > start.order &&
       cst.cst_type === CATEGORY_CST_TYPE
     )
   );
   return schema.items.filter(
     cst => (
-      cst.order > target.order &&
+      cst.order > start.order &&
       (!nextCategory || cst.order <= nextCategory.order)
     )
   );
diff --git a/rsconcept/frontend/src/models/rslang.ts b/rsconcept/frontend/src/models/rslang.ts
index 537248bf..631ca781 100644
--- a/rsconcept/frontend/src/models/rslang.ts
+++ b/rsconcept/frontend/src/models/rslang.ts
@@ -1,28 +1,44 @@
-// Module: RSLang model types
+/**
+ * Module: Models for RSLanguage.
+ */
 
-// ======== RS Parsing ============
+/**
+ * Represents formal expression.
+*/
 export interface IRSExpression {
   expression: string
 }
 
+/**
+ * Represents syntax type.
+*/
 export enum Syntax {
   UNDEF = 'undefined',
   ASCII = 'ascii',
   MATH = 'math'
 }
 
+/**
+ * Represents computability class.
+*/
 export enum ValueClass {
-  INVALID = 'invalid',
+  INVALID = 'invalid', // incalculable
   VALUE = 'value',
   PROPERTY = 'property'
 }
 
+/**
+ * Represents parsing status.
+*/
 export enum ParsingStatus {
   UNDEF = 'undefined',
   VERIFIED = 'verified',
   INCORRECT = 'incorrect'
 }
 
+/**
+ * Represents parsing error description.
+*/
 export interface IRSErrorDescription {
   errorType: RSErrorType
   position: number
@@ -30,6 +46,9 @@ export interface IRSErrorDescription {
   params: string[]
 }
 
+/**
+ * Represents AST node.
+*/
 export interface ISyntaxTreeNode {
   uid: number
   parent: number
@@ -41,17 +60,30 @@ export interface ISyntaxTreeNode {
     value: unknown
   }
 }
+
+/**
+ * Represents Syntax tree for RSLang expression.
+*/
 export type SyntaxTree = ISyntaxTreeNode[]
 
+/**
+ * Represents function argument definition.
+*/
 export interface IArgumentInfo {
   alias: string
   typification: string
 }
 
+/**
+ * Represents function argument value.
+*/
 export interface IArgumentValue extends IArgumentInfo {
   value?: string
 }
 
+/**
+ * Represents results of expression parse in RSLang.
+*/
 export interface IExpressionParse {
   parseResult: boolean
   syntax: Syntax
@@ -63,7 +95,9 @@ export interface IExpressionParse {
   args: IArgumentInfo[]
 }
 
-//! RS language token types enumeration
+/**
+ * Represents RSLang token types.
+*/
 export enum TokenID {
   // Global, local IDs and literals
   ID_LOCAL = 258,
@@ -225,26 +259,12 @@ export enum RSErrorType {
   globalFuncNoInterpretation = 34883
 }
 
-// Error handling
+/**
+ * Represents error class.
+*/
 export enum RSErrorClass {
   LEXER,
   PARSER,
   SEMANTIC,
   UNKNOWN
-}
-
-const ERRCODE_LEXER_MASK = 512;
-const ERRCODE_PARSER_MASK = 1024;
-const ERRCODE_TYPE_MASK = 2048;
-
-export function resolveErrorClass(error: RSErrorType): RSErrorClass {
-  if ((error & ERRCODE_LEXER_MASK) !== 0) {
-    return RSErrorClass.LEXER;
-  } else if ((error & ERRCODE_PARSER_MASK) !== 0) {
-    return RSErrorClass.PARSER;
-  } else if ((error & ERRCODE_TYPE_MASK) !== 0) {
-    return RSErrorClass.SEMANTIC;
-  } else {
-    return RSErrorClass.UNKNOWN;
-  }
 }
\ No newline at end of file
diff --git a/rsconcept/frontend/src/models/rslangAPI.ts b/rsconcept/frontend/src/models/rslangAPI.ts
index fe4fa0c9..05b0bc80 100644
--- a/rsconcept/frontend/src/models/rslangAPI.ts
+++ b/rsconcept/frontend/src/models/rslangAPI.ts
@@ -1,15 +1,23 @@
-// Module: RSLang model API
+/**
+ * Module: API for RSLanguage.
+ */
 
 import { applyPattern } from '../utils/utils';
 import { CstType } from './rsform';
-import { IArgumentValue } from './rslang'
+import { IArgumentValue, RSErrorClass, RSErrorType } from './rslang'
 
 const LOCALS_REGEXP = /[_a-zα-ω][a-zα-ω]*\d*/g;
 
+/**
+ * Extracts global variable names from a given expression.
+ */
 export function extractGlobals(expression: string): Set<string> {
   return new Set(expression.match(/[XCSADFPT]\d+/g) ?? []);
 }
 
+/**
+ * Infers type of constituent for a given template and arguments.
+ */
 export function inferTemplatedType(templateType: CstType, args: IArgumentValue[]): CstType {
   if (args.length === 0 || args.some(arg => !arg.value)) {
     return templateType;
@@ -20,6 +28,20 @@ export function inferTemplatedType(templateType: CstType, args: IArgumentValue[]
   }
 }
 
+/**
+ * Splits a string containing a template definition into its head and body parts.
+ *
+ * A template definition is expected to have the following format: `[head] body`.
+ * If the input string does not contain the opening square bracket '[', the entire
+ * string is treated as the body, and an empty string is assigned to the head.
+ * If the opening bracket is present, the function attempts to find the matching
+ * closing bracket ']' to determine the head and body parts.
+ *
+ * @example
+ * const template = "[header] body content";
+ * const result = splitTemplateDefinition(template);
+ * // result: `{ head: 'header', body: 'body content' }`
+ */
 export function splitTemplateDefinition(target: string) {
   let start = 0;
   for (; start < target.length && target[start] !== '['; ++start) ;
@@ -45,6 +67,13 @@ export function splitTemplateDefinition(target: string) {
   }
 }
 
+/**
+ * Substitutes values for template arguments in a given expression.
+ *
+ * This function takes an input mathematical expression and a list of argument values.
+ * It replaces template argument placeholders in the expression with their corresponding values
+ * from the provided arguments.
+ */
 export function substituteTemplateArgs(expression: string, args: IArgumentValue[]): string {
   if (args.every(arg => !arg.value)) {
     return expression;
@@ -73,3 +102,22 @@ export function substituteTemplateArgs(expression: string, args: IArgumentValue[
     return `[${head}] ${body}`
   }
 }
+
+const ERRCODE_LEXER_MASK = 512;
+const ERRCODE_PARSER_MASK = 1024;
+const ERRCODE_TYPE_MASK = 2048;
+
+/**
+ * Infers error class from error type (code).
+ */
+export function inferErrorClass(error: RSErrorType): RSErrorClass {
+  if ((error & ERRCODE_LEXER_MASK) !== 0) {
+    return RSErrorClass.LEXER;
+  } else if ((error & ERRCODE_PARSER_MASK) !== 0) {
+    return RSErrorClass.PARSER;
+  } else if ((error & ERRCODE_TYPE_MASK) !== 0) {
+    return RSErrorClass.SEMANTIC;
+  } else {
+    return RSErrorClass.UNKNOWN;
+  }
+}
\ No newline at end of file
diff --git a/rsconcept/frontend/src/pages/RSFormPage/elements/ViewSideConstituents.tsx b/rsconcept/frontend/src/pages/RSFormPage/elements/ViewSideConstituents.tsx
index aa599815..a4398495 100644
--- a/rsconcept/frontend/src/pages/RSFormPage/elements/ViewSideConstituents.tsx
+++ b/rsconcept/frontend/src/pages/RSFormPage/elements/ViewSideConstituents.tsx
@@ -13,7 +13,7 @@ import useLocalStorage from '../../../hooks/useLocalStorage';
 import useWindowSize from '../../../hooks/useWindowSize';
 import { DependencyMode as CstSource } from '../../../models/miscelanious';
 import { CstMatchMode } from '../../../models/miscelanious';
-import { applyGraphFilter } from '../../../models/miscelanious';
+import { applyGraphFilter } from '../../../models/miscelaniousAPI';
 import { CstType, IConstituenta } from '../../../models/rsform';
 import { createMockConstituenta, isMockCst, matchConstituenta } from '../../../models/rsformAPI';
 import { extractGlobals } from '../../../models/rslangAPI';
diff --git a/rsconcept/frontend/src/utils/Graph.ts b/rsconcept/frontend/src/utils/Graph.ts
index b0ec1dfa..011127ea 100644
--- a/rsconcept/frontend/src/utils/Graph.ts
+++ b/rsconcept/frontend/src/utils/Graph.ts
@@ -1,3 +1,7 @@
+/**
+ * Module: Custom graph data structure.
+ */
+
 /**
  * Represents single node of a {@link Graph}, as implemented by storing outgoing and incoming connections.
  */
diff --git a/rsconcept/frontend/src/utils/backendAPI.ts b/rsconcept/frontend/src/utils/backendAPI.ts
index d1f5a0aa..96acbdba 100644
--- a/rsconcept/frontend/src/utils/backendAPI.ts
+++ b/rsconcept/frontend/src/utils/backendAPI.ts
@@ -1,3 +1,7 @@
+/**
+ * Module: API for backend communications.
+ */
+
 import axios, { AxiosError, AxiosRequestConfig } from 'axios';
 import { toast } from 'react-toastify';
 
@@ -17,12 +21,12 @@ import {
   ICstCreateData, ICstCreatedResponse, ICstMovetoData, ICstRenameData, ICstUpdateData,
   IRSFormCreateData, IRSFormData, IRSFormUploadData} from '../models/rsform';
 import { IExpressionParse, IRSExpression } from '../models/rslang';
-import { config } from './constants';
+import { buidConstants } from './constants';
 
 const defaultOptions = {
   xsrfCookieName: 'csrftoken',
   xsrfHeaderName: 'x-csrftoken',
-  baseURL: `${config.backend}`,
+  baseURL: `${buidConstants.backend}`,
   withCredentials: true
 }
 
diff --git a/rsconcept/frontend/src/utils/codemirror.ts b/rsconcept/frontend/src/utils/codemirror.ts
index 0d028d24..e23daeee 100644
--- a/rsconcept/frontend/src/utils/codemirror.ts
+++ b/rsconcept/frontend/src/utils/codemirror.ts
@@ -1,3 +1,7 @@
+/**
+ * Module: CodeMirror customizations.
+ */
+
 import { syntaxTree } from '@codemirror/language'
 import { NodeType, Tree, TreeCursor } from '@lezer/common'
 import { ReactCodeMirrorRef, SelectionRange } from '@uiw/react-codemirror'
diff --git a/rsconcept/frontend/src/utils/color.ts b/rsconcept/frontend/src/utils/color.ts
index cf046bd1..230a1ea5 100644
--- a/rsconcept/frontend/src/utils/color.ts
+++ b/rsconcept/frontend/src/utils/color.ts
@@ -1,11 +1,15 @@
-// =========== Modules contains all dynamic color definitions ==========
+/**
+ * Module: Single place for all color definitions in code (see index.css for full defs).
+ */
 
 import { GramData, Grammeme, NounGrams, PartOfSpeech, VerbGrams } from '../models/language'
 import { CstClass, ExpressionStatus } from '../models/rsform'
 import { ISyntaxTreeNode, TokenID } from '../models/rslang'
 
 
-// ============= MAIN COLOR THEMES ==========
+/**
+ * Represents application color theme configuration.
+ */
 export interface IColorTheme {  
   bgDefault: string
   bgInput: string
@@ -39,7 +43,9 @@ export interface IColorTheme {
   fgOrange: string
 }
 
-// ======= Light =======
+/**
+ * Represents application Light theme.
+ */
 export const lightT: IColorTheme = {
   bgDefault:  'var(--cl-bg-100)',
   bgInput:    'var(--cl-bg-120)',
@@ -73,7 +79,9 @@ export const lightT: IColorTheme = {
   fgOrange:   'hsl(030, 090%, 055%)'
 };
 
-// ======= DARK ========
+/**
+ * Represents application Dark theme.
+ */
 export const darkT: IColorTheme = {
   bgDefault:  'var(--cd-bg-100)',
   bgInput:    'var(--cd-bg-120)',
@@ -107,7 +115,9 @@ export const darkT: IColorTheme = {
   fgOrange:   'hsl(035, 100%, 050%)'
 };
 
-// ============ SELECT THEMES ==========
+/**
+ * Represents Select component Light theme.
+ */
 export const selectLightT = {
   primary: lightT.bgPrimary,
   primary75: lightT.bgSelected,
@@ -130,6 +140,9 @@ export const selectLightT = {
   neutral90: lightT.fgWarning
 }
 
+/**
+ * Represents Select component Dark theme.
+ */
 export const selectDarkT = {
   primary: darkT.bgPrimary,
   primary75: darkT.bgSelected,
@@ -152,7 +165,9 @@ export const selectDarkT = {
   neutral90: darkT.fgWarning
 }
 
-// ============ GRAPH THEMES ==========
+/**
+ * Represents Graph component Light theme.
+ */
 export const graphLightT = {
   canvas: {
     background: '#f9fafb',
@@ -202,6 +217,9 @@ export const graphLightT = {
   }
 }
 
+/**
+ * Represents Graph component Dark theme.
+ */
 export const graphDarkT = {
   canvas: {
     background: '#171717' // var(--cd-bg-100)
@@ -251,7 +269,9 @@ export const graphDarkT = {
   }
 }
 
-// ======== Bracket Matching Themes ===========
+/**
+ * Represents Brackets highlights Light theme.
+ */
 export const bracketsLightT = {
   '.cc-nonmatchingBracket': {
     color: lightT.fgRed,
@@ -263,6 +283,9 @@ export const bracketsLightT = {
   },
 };
 
+/**
+ * Represents Brackets highlights Dark theme.
+ */
 export const bracketsDarkT = {
   '.cc-nonmatchingBracket': {
     color: darkT.fgRed,
@@ -274,7 +297,9 @@ export const bracketsDarkT = {
   },
 };
 
-// =========== Misc colors ======================
+/**
+ * Determines background color for {@link ISyntaxTreeNode} based on its type.
+ */
 export function colorbgSyntaxTree(node: ISyntaxTreeNode, colors: IColorTheme): string {
   switch (node.typeID) {
   case TokenID.PUNC_DEFINE:
@@ -354,6 +379,9 @@ export function colorbgSyntaxTree(node: ISyntaxTreeNode, colors: IColorTheme): s
   return colors.bgRed;
 }
 
+/**
+ * Determines background color for {@link ExpressionStatus}.
+ */
 export function colorbgCstStatus(status: ExpressionStatus, colors: IColorTheme): string {
   switch (status) {
     case ExpressionStatus.VERIFIED: return colors.bgGreen;
@@ -365,6 +393,9 @@ export function colorbgCstStatus(status: ExpressionStatus, colors: IColorTheme):
   }
 }
 
+/**
+ * Determines foreground color for {@link ExpressionStatus}.
+ */
 export function colorfgCstStatus(status: ExpressionStatus, colors: IColorTheme): string {
   switch (status) {
     case ExpressionStatus.VERIFIED: return colors.fgGreen;
@@ -376,6 +407,9 @@ export function colorfgCstStatus(status: ExpressionStatus, colors: IColorTheme):
   }
 }
 
+/**
+ * Determines background color for {@link IConstituenta} depending on its {@link CstClass}.
+ */
 export function colorbgCstClass(cstClass: CstClass, colors: IColorTheme): string {
   switch (cstClass) {
     case CstClass.BASIC: return colors.bgGreen;
@@ -385,6 +419,25 @@ export function colorbgCstClass(cstClass: CstClass, colors: IColorTheme): string
   }
 }
 
+/**
+ * Determines background color for {@link GramData}.
+ */
+export function colorbgGrammeme(gram: GramData, colors: IColorTheme): string {
+  if (PartOfSpeech.includes(gram as Grammeme)) {
+    return colors.bgBlue;
+  }
+  if (NounGrams.includes(gram as Grammeme)) {
+    return colors.bgGreen;
+  }
+  if (VerbGrams.includes(gram as Grammeme)) {
+    return colors.bgTeal;
+  }
+  return colors.bgInput;
+}
+
+/**
+ * Determines foreground color for {@link GramData}.
+ */
 export function colorfgGrammeme(gram: GramData, colors: IColorTheme): string {
   if (PartOfSpeech.includes(gram as Grammeme)) {
     return colors.fgBlue;
@@ -401,17 +454,3 @@ export function colorfgGrammeme(gram: GramData, colors: IColorTheme): string {
     return colors.fgPurple;
   }
 }
-
-export function colorbgGrammeme(gram: GramData, colors: IColorTheme): string {
-  if (PartOfSpeech.includes(gram as Grammeme)) {
-    return colors.bgBlue;
-  }
-  if (NounGrams.includes(gram as Grammeme)) {
-    return colors.bgGreen;
-  }
-  if (VerbGrams.includes(gram as Grammeme)) {
-    return colors.bgTeal;
-  }
-  return colors.bgInput;
-}
-
diff --git a/rsconcept/frontend/src/utils/constants.ts b/rsconcept/frontend/src/utils/constants.ts
index 2c1cc72b..09374c7c 100644
--- a/rsconcept/frontend/src/utils/constants.ts
+++ b/rsconcept/frontend/src/utils/constants.ts
@@ -1,16 +1,47 @@
-// Constants
-export const config = {
+/**
+ * Module: Global constants.
+ */
+
+/**
+ * Variable constants depending on build type.
+ */
+export const buidConstants = {
   backend: import.meta.env.VITE_PORTAL_BACKEND as string
 };
+
+/**
+ * General UI timeout [in ms] for waiting for render.
+ */
 export const TIMEOUT_UI_REFRESH = 100;
+
+/**
+ * Timeout [in ms] for graph refresh.
+ */
 export const TIMEOUT_GRAPH_REFRESH = 200;
 
+/**
+ * Exteor file extension for RSForm.
+ */
 export const EXTEOR_TRS_FILE = '.trs';
 
+/**
+ * Resource relative URIs.
+ */
+export const resources = {
+  graph_font: '/DejaVu.ttf'
+}
+
+
+/**
+ * Youtube IDs for embedding.
+ */
 export const youtube = {
   intro: '0Ty9mu9sOJo'
 };
 
+/**
+ * Constant URLs.
+ */
 export const urls = {
   concept: 'https://www.acconcept.ru/',
   exteor32: 'https://drive.google.com/open?id=1IHlMMwaYlAUBRSxU1RU_hXM5mFU9-oyK&usp=drive_fs',
@@ -24,14 +55,16 @@ export const urls = {
   restapi: 'https://api.portal.acconcept.ru'
 };
 
-export const resources = {
-  graph_font: '/DejaVu.ttf'
-}
-
+/**
+ * Global unique IDs.
+ */
 export const globalIDs = {
   main_scroll: 'main-scroll'
 }
 
+/**
+ * Prefixes for generating unique keys for lists.
+ */
 export const prefixes = {
   cst_list: 'cst-list-',
   cst_hidden_list: 'cst-hidden-list-',
diff --git a/rsconcept/frontend/src/utils/labels.ts b/rsconcept/frontend/src/utils/labels.ts
index ad4fd777..b80e34ee 100644
--- a/rsconcept/frontend/src/utils/labels.ts
+++ b/rsconcept/frontend/src/utils/labels.ts
@@ -1,10 +1,17 @@
-// =========== Module contains all text descriptors. ==========
-
+/**
+ * Module: Text descriptors for UI and model elements.
+ * 
+ * Label is a short text used to represent an entity.
+ * Description is a long description used in tooltips.
+ */
 import { GramData,Grammeme, ReferenceType } from '../models/language';
 import { CstMatchMode, DependencyMode, HelpTopic, LibraryFilterStrategy } from '../models/miscelanious';
 import { CstClass, CstType, ExpressionStatus, IConstituenta } from '../models/rsform';
 import { IArgumentInfo, IRSErrorDescription, ISyntaxTreeNode, ParsingStatus, RSErrorType, TokenID } from '../models/rslang';
 
+/**
+ * Generates desription for {@link IConstituenta}.
+ */
 export function describeConstituenta(cst: IConstituenta): string {
   if (cst.cst_type === CstType.STRUCTURED) {
     return (
@@ -23,7 +30,10 @@ export function describeConstituenta(cst: IConstituenta): string {
   }
 }
 
-export function describeConstituentaTerm(cst: IConstituenta | undefined): string {
+/**
+ * Generates desription for term of a given {@link IConstituenta}.
+ */
+export function describeConstituentaTerm(cst?: IConstituenta): string {
   if (!cst) {
     return '!Конституента отсутствует!';
   }
@@ -34,10 +44,16 @@ export function describeConstituentaTerm(cst: IConstituenta | undefined): string
   }
 }
 
+/**
+ * Generates label for {@link IConstituenta}.
+ */
 export function labelConstituenta(cst: IConstituenta) {
   return `${cst.alias}: ${describeConstituenta(cst)}`;
 }
 
+/**
+ * Retrieves label for {@link TokenID}.
+ */
 export function labelToken(id: TokenID): string {
   switch (id) {
   case TokenID.BOOLEAN:       return 'ℬ()';
@@ -126,6 +142,9 @@ export function describeToken(id: TokenID): string {
   return `no description: ${id}`;
 }
 
+/**
+ * Retrieves label for {@link CstMatchMode}.
+ */
 export function labelCstMathchMode(mode: CstMatchMode): string {
   switch (mode) {
     case CstMatchMode.ALL:  return 'общий';
@@ -136,6 +155,9 @@ export function labelCstMathchMode(mode: CstMatchMode): string {
   }
 }
 
+/**
+ * Retrieves description for {@link CstMatchMode}.
+ */
 export function describeCstMathchMode(mode: CstMatchMode): string {
   switch (mode) {
     case CstMatchMode.ALL:  return 'искать во всех атрибутах';
@@ -146,6 +168,9 @@ export function describeCstMathchMode(mode: CstMatchMode): string {
   }
 }
 
+/**
+ * Retrieves label for {@link DependencyMode}.
+ */
 export function labelCstSource(mode: DependencyMode): string {
   switch (mode) {
     case DependencyMode.ALL:            return 'не ограничен';
@@ -157,6 +182,9 @@ export function labelCstSource(mode: DependencyMode): string {
   }
 }
 
+/**
+ * Retrieves description for {@link DependencyMode}.
+ */
 export function describeCstSource(mode: DependencyMode): string {
   switch (mode) {
     case DependencyMode.ALL:            return 'все конституенты';
@@ -168,6 +196,9 @@ export function describeCstSource(mode: DependencyMode): string {
   }
 }
 
+/**
+ * Retrieves label for {@link LibraryFilterStrategy}.
+ */
 export function labelLibraryFilter(strategy: LibraryFilterStrategy): string {
   switch (strategy) {
     case LibraryFilterStrategy.MANUAL:      return 'отображать все';
@@ -179,6 +210,9 @@ export function labelLibraryFilter(strategy: LibraryFilterStrategy): string {
   }
 }
 
+/**
+ * Retrieves description for {@link LibraryFilterStrategy}.
+ */
 export function describeLibraryFilter(strategy: LibraryFilterStrategy): string {
   switch (strategy) {
     case LibraryFilterStrategy.MANUAL:      return 'Отображать все схемы';
@@ -190,6 +224,9 @@ export function describeLibraryFilter(strategy: LibraryFilterStrategy): string {
   }
 }
 
+/**
+ * Retrieves label for graph layout mode.
+ */
 export const mapLableLayout: Map<string, string> = 
 new Map([
   ['forceatlas2', 'Граф: Атлас 2D'],
@@ -207,6 +244,9 @@ new Map([
   ['nooverlap', 'Граф: Без перекрытия']
 ]);
 
+/**
+ * Retrieves label for graph coloring mode.
+ */
 export const mapLabelColoring: Map<string, string> = 
 new Map([
   ['none', 'Цвет: моно'],
@@ -214,6 +254,9 @@ new Map([
   ['type', 'Цвет: класс'],
 ]);
 
+/**
+ * Retrieves label for {@link ExpressionStatus}.
+ */
 export function labelExpressionStatus(status: ExpressionStatus): string {
   switch (status) {
     case ExpressionStatus.VERIFIED:     return 'корректно';
@@ -225,6 +268,9 @@ export function labelExpressionStatus(status: ExpressionStatus): string {
   }
 }
 
+/**
+ * Retrieves description for {@link ExpressionStatus}.
+ */
 export function describeExpressionStatus(status: ExpressionStatus): string {
   switch (status) {
     case ExpressionStatus.VERIFIED:     return 'выражение корректно и вычислимо';
@@ -236,6 +282,9 @@ export function describeExpressionStatus(status: ExpressionStatus): string {
   }
 }
 
+/**
+ * Retrieves label for {@link HelpTopic}.
+ */
 export function labelHelpTopic(topic: HelpTopic): string {
   switch (topic) {
     case HelpTopic.MAIN:          return 'Портал';
@@ -252,6 +301,9 @@ export function labelHelpTopic(topic: HelpTopic): string {
   }
 }
 
+/**
+ * Retrieves description for {@link HelpTopic}.
+ */
 export function describeHelpTopic(topic: HelpTopic): string {
   switch (topic) {
     case HelpTopic.MAIN:          return 'Общая справка по порталу';
@@ -268,6 +320,9 @@ export function describeHelpTopic(topic: HelpTopic): string {
   }
 }
 
+/**
+ * Retrieves label for {@link CstType}.
+ */
 export function labelCstType(type: CstType): string {
   switch (type) {
     case CstType.BASE:          return 'Базисное множество';
@@ -281,6 +336,9 @@ export function labelCstType(type: CstType): string {
   }
 }
 
+/**
+ * Retrieves label for {@link ReferenceType}.
+ */
 export function labelReferenceType(type: ReferenceType): string {
   switch(type) {
     case ReferenceType.ENTITY:    return 'Использование термина';
@@ -288,6 +346,9 @@ export function labelReferenceType(type: ReferenceType): string {
   }
 }
 
+/**
+ * Retrieves label for {@link CstClass}.
+ */
 export function labelCstClass(cclass: CstClass): string {
   switch (cclass) {
     case CstClass.BASIC:        return 'базовый';
@@ -297,6 +358,9 @@ export function labelCstClass(cclass: CstClass): string {
   }
 }
 
+/**
+ * Retrieves description for {@link CstClass}.
+ */
 export function describeCstClass(cclass: CstClass): string {
   switch (cclass) {
     case CstClass.BASIC:        return 'неопределяемое понятие, требует конвенции';
@@ -306,6 +370,9 @@ export function describeCstClass(cclass: CstClass): string {
   }
 }
 
+/**
+ * Generates label for typification.
+ */
 export function labelTypification({ isValid, resultType, args }: {
   isValid: boolean;
   resultType: string;
@@ -332,6 +399,9 @@ export function labelCstTypification(cst: IConstituenta): string {
   });
 }
 
+/**
+ * Generates label for {@link ISyntaxTreeNode}.
+ */
 export function labelSyntaxTree(node: ISyntaxTreeNode): string {
   switch (node.typeID) {
     case TokenID.ID_LOCAL:
@@ -481,6 +551,9 @@ export function labelGrammeme(gram: GramData): string {
   }
 }
 
+/**
+ * Generates error description for {@link IRSErrorDescription}.
+ */
 export function describeRSError(error: IRSErrorDescription): string {
   switch (error.errorType) {
   case RSErrorType.unknownSymbol:
diff --git a/rsconcept/frontend/src/utils/misc.ts b/rsconcept/frontend/src/utils/misc.ts
index 8e093b5b..9c55fa60 100644
--- a/rsconcept/frontend/src/utils/misc.ts
+++ b/rsconcept/frontend/src/utils/misc.ts
@@ -1,9 +1,10 @@
-
-// Module: miscellaneous static functions to generate UI resources
+/**
+ * Module: miscellaneous static functions to generate UI resources.
+ */
 
 import { CstType, IConstituenta, IRSForm } from '../models/rsform';
-import { IRSErrorDescription } from '../models/rslang';
-import { resolveErrorClass, RSErrorClass } from '../models/rslang';
+import { IRSErrorDescription, RSErrorClass } from '../models/rslang';
+import { inferErrorClass } from '../models/rslangAPI';
 import { labelCstType } from './labels';
 
 export function getCstTypePrefix(type: CstType) {
@@ -70,7 +71,7 @@ export function cloneTitle(schema: IRSForm): string {
 
 export function getRSErrorPrefix(error: IRSErrorDescription): string {
   const id = error.errorType.toString(16)
-  switch(resolveErrorClass(error.errorType)) {
+  switch(inferErrorClass(error.errorType)) {
   case RSErrorClass.LEXER: return 'L' + id;
   case RSErrorClass.PARSER: return 'P' + id;
   case RSErrorClass.SEMANTIC: return 'S' + id;
diff --git a/rsconcept/frontend/src/utils/selectors.ts b/rsconcept/frontend/src/utils/selectors.ts
index 352ab492..09ccaf32 100644
--- a/rsconcept/frontend/src/utils/selectors.ts
+++ b/rsconcept/frontend/src/utils/selectors.ts
@@ -1,4 +1,6 @@
-// Module: Selector maps
+/**
+ * Module: Mappings for selector UI elements.
+ */
 import { LayoutTypes } from 'reagraph';
 
 import { type GramData, Grammeme, ReferenceType } from '../models/language';
diff --git a/rsconcept/frontend/src/utils/utils.tsx b/rsconcept/frontend/src/utils/utils.tsx
index 926a209d..93ac1c2b 100644
--- a/rsconcept/frontend/src/utils/utils.tsx
+++ b/rsconcept/frontend/src/utils/utils.tsx
@@ -1,6 +1,13 @@
+/**
+ * Module: Utility functions.
+ */
+
+/**
+ * Checks if arguments is Node.
+ */
 export function assertIsNode(e: EventTarget | null): asserts e is Node {
-  if (!e || !('nodeType' in e)) {
-    throw new Error('Node expected');
+  if (e === null || !('nodeType' in e)) {
+    throw new TypeError(`Expected 'Node' but recieved '${e?.constructor.name ?? 'null'}'`);
   }
 }