File: //home/arjun/projects/buyercall/node_modules/@ckeditor/ckeditor5-engine/src/view/stylesmap.js
/**
* @license Copyright (c) 2003-2022, CKSource Holding sp. z o.o. All rights reserved.
* For licensing, see LICENSE.md or https://ckeditor.com/legal/ckeditor-oss-license
*/
/**
* @module engine/view/stylesmap
*/
import { get, isObject, merge, set, unset } from 'lodash-es';
/**
* Styles map. Allows handling (adding, removing, retrieving) a set of style rules (usually, of an element).
*
* The styles map is capable of normalizing style names so e.g. the following operations are possible:
*/
export default class StylesMap {
/**
* Creates Styles instance.
*
* @param {module:engine/view/stylesmap~StylesProcessor} styleProcessor
*/
constructor( styleProcessor ) {
/**
* Keeps an internal representation of styles map. Normalized styles are kept as object tree to allow unified modification and
* value access model using lodash's get, set, unset, etc methods.
*
* When no style processor rules are defined it acts as simple key-value storage.
*
* @private
* @type {Object}
*/
this._styles = {};
/**
* An instance of the {@link module:engine/view/stylesmap~StylesProcessor}.
*
* @private
* @member {module:engine/view/stylesmap~StylesProcessor}
*/
this._styleProcessor = styleProcessor;
}
/**
* Returns true if style map has no styles set.
*
* @type {Boolean}
*/
get isEmpty() {
const entries = Object.entries( this._styles );
const from = Array.from( entries );
return !from.length;
}
/**
* Number of styles defined.
*
* @type {Number}
*/
get size() {
if ( this.isEmpty ) {
return 0;
}
return this.getStyleNames().length;
}
/**
* Set styles map to a new value.
*
* styles.setTo( 'border:1px solid blue;margin-top:1px;' );
*
* @param {String} inlineStyle
*/
setTo( inlineStyle ) {
this.clear();
const parsedStyles = Array.from( parseInlineStyles( inlineStyle ).entries() );
for ( const [ key, value ] of parsedStyles ) {
this._styleProcessor.toNormalizedForm( key, value, this._styles );
}
}
/**
* Checks if a given style is set.
*
* styles.setTo( 'margin-left:1px;' );
*
* styles.has( 'margin-left' ); // -> true
* styles.has( 'padding' ); // -> false
*
* **Note**: This check supports normalized style names.
*
* // Enable 'margin' shorthand processing:
* editor.data.addStyleProcessorRules( addMarginRules );
*
* styles.setTo( 'margin:2px;' );
*
* styles.has( 'margin' ); // -> true
* styles.has( 'margin-top' ); // -> true
* styles.has( 'margin-left' ); // -> true
*
* styles.remove( 'margin-top' );
*
* styles.has( 'margin' ); // -> false
* styles.has( 'margin-top' ); // -> false
* styles.has( 'margin-left' ); // -> true
*
* @param {String} name Style name.
* @returns {Boolean}
*/
has( name ) {
if ( this.isEmpty ) {
return false;
}
const styles = this._styleProcessor.getReducedForm( name, this._styles );
const propertyDescriptor = styles.find( ( [ property ] ) => property === name );
// Only return a value if it is set;
return Array.isArray( propertyDescriptor );
}
/**
* Sets a given style.
*
* Can insert one by one:
*
* styles.set( 'color', 'blue' );
* styles.set( 'margin-right', '1em' );
*
* or many styles at once:
*
* styles.set( {
* color: 'blue',
* 'margin-right': '1em'
* } );
*
* ***Note**:* This method uses {@link module:engine/controller/datacontroller~DataController#addStyleProcessorRules
* enabled style processor rules} to normalize passed values.
*
* // Enable 'margin' shorthand processing:
* editor.data.addStyleProcessorRules( addMarginRules );
*
* styles.set( 'margin', '2px' );
*
* The above code will set margin to:
*
* styles.getNormalized( 'margin' );
* // -> { top: '2px', right: '2px', bottom: '2px', left: '2px' }
*
* Which makes it possible to retrieve a "sub-value":
*
* styles.get( 'margin-left' ); // -> '2px'
*
* Or modify it:
*
* styles.remove( 'margin-left' );
*
* styles.getNormalized( 'margin' ); // -> { top: '1px', bottom: '1px', right: '1px' }
* styles.toString(); // -> 'margin-bottom:1px;margin-right:1px;margin-top:1px;'
*
* This method also allows to set normalized values directly (if a particular styles processor rule was enabled):
*
* styles.set( 'border-color', { top: 'blue' } );
* styles.set( 'margin', { right: '2em' } );
*
* styles.toString(); // -> 'border-color-top:blue;margin-right:2em;'
*
* @param {String|Object} nameOrObject Style property name or object with multiple properties.
* @param {String|Object} valueOrObject Value to set.
*/
set( nameOrObject, valueOrObject ) {
if ( isObject( nameOrObject ) ) {
for ( const [ key, value ] of Object.entries( nameOrObject ) ) {
this._styleProcessor.toNormalizedForm( key, value, this._styles );
}
} else {
this._styleProcessor.toNormalizedForm( nameOrObject, valueOrObject, this._styles );
}
}
/**
* Removes given style.
*
* styles.setTo( 'background:#f00;margin-right:2px;' );
*
* styles.remove( 'background' );
*
* styles.toString(); // -> 'margin-right:2px;'
*
* ***Note**:* This method uses {@link module:engine/controller/datacontroller~DataController#addStyleProcessorRules
* enabled style processor rules} to normalize passed values.
*
* // Enable 'margin' shorthand processing:
* editor.data.addStyleProcessorRules( addMarginRules );
*
* styles.setTo( 'margin:1px' );
*
* styles.remove( 'margin-top' );
* styles.remove( 'margin-right' );
*
* styles.toString(); // -> 'margin-bottom:1px;margin-left:1px;'
*
* @param {String} name Style name.
*/
remove( name ) {
const path = toPath( name );
unset( this._styles, path );
delete this._styles[ name ];
this._cleanEmptyObjectsOnPath( path );
}
/**
* Returns a normalized style object or a single value.
*
* // Enable 'margin' shorthand processing:
* editor.data.addStyleProcessorRules( addMarginRules );
*
* const styles = new Styles();
* styles.setTo( 'margin:1px 2px 3em;' );
*
* styles.getNormalized( 'margin' );
* // will log:
* // {
* // top: '1px',
* // right: '2px',
* // bottom: '3em',
* // left: '2px' // normalized value from margin shorthand
* // }
*
* styles.getNormalized( 'margin-left' ); // -> '2px'
*
* **Note**: This method will only return normalized styles if a style processor was defined.
*
* @param {String} name Style name.
* @returns {Object|String|undefined}
*/
getNormalized( name ) {
return this._styleProcessor.getNormalized( name, this._styles );
}
/**
* Returns a normalized style string. Styles are sorted by name.
*
* styles.set( 'margin' , '1px' );
* styles.set( 'background', '#f00' );
*
* styles.toString(); // -> 'background:#f00;margin:1px;'
*
* **Note**: This method supports normalized styles if defined.
*
* // Enable 'margin' shorthand processing:
* editor.data.addStyleProcessorRules( addMarginRules );
*
* styles.set( 'margin' , '1px' );
* styles.set( 'background', '#f00' );
* styles.remove( 'margin-top' );
* styles.remove( 'margin-right' );
*
* styles.toString(); // -> 'background:#f00;margin-bottom:1px;margin-left:1px;'
*
* @returns {String}
*/
toString() {
if ( this.isEmpty ) {
return '';
}
return this._getStylesEntries()
.map( arr => arr.join( ':' ) )
.sort()
.join( ';' ) + ';';
}
/**
* Returns property as a value string or undefined if property is not set.
*
* // Enable 'margin' shorthand processing:
* editor.data.addStyleProcessorRules( addMarginRules );
*
* const styles = new Styles();
* styles.setTo( 'margin:1px;' );
* styles.set( 'margin-bottom', '3em' );
*
* styles.getAsString( 'margin' ); // -> 'margin: 1px 1px 3em;'
*
* Note, however, that all sub-values must be set for the longhand property name to return a value:
*
* const styles = new Styles();
* styles.setTo( 'margin:1px;' );
* styles.remove( 'margin-bottom' );
*
* styles.getAsString( 'margin' ); // -> undefined
*
* In the above scenario, it is not possible to return a `margin` value, so `undefined` is returned.
* Instead, you should use:
*
* const styles = new Styles();
* styles.setTo( 'margin:1px;' );
* styles.remove( 'margin-bottom' );
*
* for ( const styleName of styles.getStyleNames() ) {
* console.log( styleName, styles.getAsString( styleName ) );
* }
* // 'margin-top', '1px'
* // 'margin-right', '1px'
* // 'margin-left', '1px'
*
* In general, it is recommend to iterate over style names like in the example above. This way, you will always get all
* the currently set style values. So, if all the 4 margin values would be set
* the for-of loop above would yield only `'margin'`, `'1px'`:
*
* const styles = new Styles();
* styles.setTo( 'margin:1px;' );
*
* for ( const styleName of styles.getStyleNames() ) {
* console.log( styleName, styles.getAsString( styleName ) );
* }
* // 'margin', '1px'
*
* **Note**: To get a normalized version of a longhand property use the {@link #getNormalized `#getNormalized()`} method.
*
* @param {String} propertyName
* @returns {String|undefined}
*/
getAsString( propertyName ) {
if ( this.isEmpty ) {
return;
}
if ( this._styles[ propertyName ] && !isObject( this._styles[ propertyName ] ) ) {
// Try return styles set directly - values that are not parsed.
return this._styles[ propertyName ];
}
const styles = this._styleProcessor.getReducedForm( propertyName, this._styles );
const propertyDescriptor = styles.find( ( [ property ] ) => property === propertyName );
// Only return a value if it is set;
if ( Array.isArray( propertyDescriptor ) ) {
return propertyDescriptor[ 1 ];
}
}
/**
* Returns all style properties names as they would appear when using {@link #toString `#toString()`}.
*
* When `expand` is set to true and there's a shorthand style property set, it will also return all equivalent styles:
*
* stylesMap.setTo( 'margin: 1em' )
*
* will be expanded to:
*
* [ 'margin', 'margin-top', 'margin-right', 'margin-bottom', 'margin-left' ]
*
* @param {Boolean} [expand=false] Expand shorthand style properties and all return equivalent style representations.
* @returns {Array.<String>}
*/
getStyleNames( expand = false ) {
if ( this.isEmpty ) {
return [];
}
if ( expand ) {
return this._styleProcessor.getStyleNames( this._styles );
}
const entries = this._getStylesEntries();
return entries.map( ( [ key ] ) => key );
}
/**
* Removes all styles.
*/
clear() {
this._styles = {};
}
/**
* Returns normalized styles entries for further processing.
*
* @private
* @returns {Array.<module:engine/view/stylesmap~PropertyDescriptor>}
*/
_getStylesEntries() {
const parsed = [];
const keys = Object.keys( this._styles );
for ( const key of keys ) {
parsed.push( ...this._styleProcessor.getReducedForm( key, this._styles ) );
}
return parsed;
}
/**
* Removes empty objects upon removing an entry from internal object.
*
* @param {String} path
* @private
*/
_cleanEmptyObjectsOnPath( path ) {
const pathParts = path.split( '.' );
const isChildPath = pathParts.length > 1;
if ( !isChildPath ) {
return;
}
const parentPath = pathParts.splice( 0, pathParts.length - 1 ).join( '.' );
const parentObject = get( this._styles, parentPath );
if ( !parentObject ) {
return;
}
const isParentEmpty = !Array.from( Object.keys( parentObject ) ).length;
if ( isParentEmpty ) {
this.remove( parentPath );
}
}
}
/**
* Style processor is responsible for writing and reading a normalized styles object.
*/
export class StylesProcessor {
/**
* Creates StylesProcessor instance.
*
* @private
*/
constructor() {
this._normalizers = new Map();
this._extractors = new Map();
this._reducers = new Map();
this._consumables = new Map();
}
/**
* Parse style string value to a normalized object and appends it to styles object.
*
* const styles = {};
*
* stylesProcessor.toNormalizedForm( 'margin', '1px', styles );
*
* // styles will consist: { margin: { top: '1px', right: '1px', bottom: '1px', left: '1px; } }
*
* **Note**: To define normalizer callbacks use {@link #setNormalizer}.
*
* @param {String} name Name of style property.
* @param {String} propertyValue Value of style property.
* @param {Object} styles Object holding normalized styles.
*/
toNormalizedForm( name, propertyValue, styles ) {
if ( isObject( propertyValue ) ) {
appendStyleValue( styles, toPath( name ), propertyValue );
return;
}
if ( this._normalizers.has( name ) ) {
const normalizer = this._normalizers.get( name );
const { path, value } = normalizer( propertyValue );
appendStyleValue( styles, path, value );
} else {
appendStyleValue( styles, name, propertyValue );
}
}
/**
* Returns a normalized version of a style property.
* const styles = {
* margin: { top: '1px', right: '1px', bottom: '1px', left: '1px; },
* background: { color: '#f00' }
* };
*
* stylesProcessor.getNormalized( 'background' );
* // will return: { color: '#f00' }
*
* stylesProcessor.getNormalized( 'margin-top' );
* // will return: '1px'
*
* **Note**: In some cases extracting single value requires defining an extractor callback {@link #setExtractor}.
*
* @param {String} name Name of style property.
* @param {Object} styles Object holding normalized styles.
* @returns {*}
*/
getNormalized( name, styles ) {
if ( !name ) {
return merge( {}, styles );
}
// Might be empty string.
if ( styles[ name ] !== undefined ) {
return styles[ name ];
}
if ( this._extractors.has( name ) ) {
const extractor = this._extractors.get( name );
if ( typeof extractor === 'string' ) {
return get( styles, extractor );
}
const value = extractor( name, styles );
if ( value ) {
return value;
}
}
return get( styles, toPath( name ) );
}
/**
* Returns a reduced form of style property form normalized object.
*
* For default margin reducer, the below code:
*
* stylesProcessor.getReducedForm( 'margin', {
* margin: { top: '1px', right: '1px', bottom: '2px', left: '1px; }
* } );
*
* will return:
*
* [
* [ 'margin', '1px 1px 2px' ]
* ]
*
* because it might be represented as a shorthand 'margin' value. However if one of margin long hand values is missing it should return:
*
* [
* [ 'margin-top', '1px' ],
* [ 'margin-right', '1px' ],
* [ 'margin-bottom', '2px' ]
* // the 'left' value is missing - cannot use 'margin' shorthand.
* ]
*
* **Note**: To define reducer callbacks use {@link #setReducer}.
*
* @param {String} name Name of style property.
* @param {Object} styles Object holding normalized styles.
* @returns {Array.<module:engine/view/stylesmap~PropertyDescriptor>}
*/
getReducedForm( name, styles ) {
const normalizedValue = this.getNormalized( name, styles );
// Might be empty string.
if ( normalizedValue === undefined ) {
return [];
}
if ( this._reducers.has( name ) ) {
const reducer = this._reducers.get( name );
return reducer( normalizedValue );
}
return [ [ name, normalizedValue ] ];
}
/**
* Return all style properties. Also expand shorthand properties (e.g. `margin`, `background`) if respective extractor is available.
*
* @param {Object} styles Object holding normalized styles.
* @returns {Array.<String>}
*/
getStyleNames( styles ) {
// Find all extractable styles that have a value.
const expandedStyleNames = Array.from( this._consumables.keys() ).filter( name => {
const style = this.getNormalized( name, styles );
if ( style && typeof style == 'object' ) {
return Object.keys( style ).length;
}
return style;
} );
// For simple styles (for example `color`) we don't have a map of those styles
// but they are 1 to 1 with normalized object keys.
const styleNamesKeysSet = new Set( [
...expandedStyleNames,
...Object.keys( styles )
] );
return Array.from( styleNamesKeysSet.values() );
}
/**
* Returns related style names.
*
* stylesProcessor.getRelatedStyles( 'margin' );
* // will return: [ 'margin-top', 'margin-right', 'margin-bottom', 'margin-left' ];
*
* stylesProcessor.getRelatedStyles( 'margin-top' );
* // will return: [ 'margin' ];
*
* **Note**: To define new style relations load an existing style processor or use
* {@link module:engine/view/stylesmap~StylesProcessor#setStyleRelation `StylesProcessor.setStyleRelation()`}.
*
* @param {String} name
* @returns {Array.<String>}
*/
getRelatedStyles( name ) {
return this._consumables.get( name ) || [];
}
/**
* Adds a normalizer method for a style property.
*
* A normalizer returns describing how the value should be normalized.
*
* For instance 'margin' style is a shorthand for four margin values:
*
* - 'margin-top'
* - 'margin-right'
* - 'margin-bottom'
* - 'margin-left'
*
* and can be written in various ways if some values are equal to others. For instance `'margin: 1px 2em;'` is a shorthand for
* `'margin-top: 1px;margin-right: 2em;margin-bottom: 1px;margin-left: 2em'`.
*
* A normalizer should parse various margin notations as a single object:
*
* const styles = {
* margin: {
* top: '1px',
* right: '2em',
* bottom: '1px',
* left: '2em'
* }
* };
*
* Thus a normalizer for 'margin' style should return an object defining style path and value to store:
*
* const returnValue = {
* path: 'margin',
* value: {
* top: '1px',
* right: '2em',
* bottom: '1px',
* left: '2em'
* }
* };
*
* Additionally to fully support all margin notations there should be also defined 4 normalizers for longhand margin notations. Below
* is an example for 'margin-top' style property normalizer:
*
* stylesProcessor.setNormalizer( 'margin-top', valueString => {
* return {
* path: 'margin.top',
* value: valueString
* }
* } );
*
* @param {String} name
* @param {Function} callback
*/
setNormalizer( name, callback ) {
this._normalizers.set( name, callback );
}
/**
* Adds a extractor callback for a style property.
*
* Most normalized style values are stored as one level objects. It is assumed that `'margin-top'` style will be stored as:
*
* const styles = {
* margin: {
* top: 'value'
* }
* }
*
* However, some styles can have conflicting notations and thus it might be harder to extract a style value from shorthand. For instance
* the 'border-top-style' can be defined using `'border-top:solid'`, `'border-style:solid none none none'` or by `'border:solid'`
* shorthands. The default border styles processors stores styles as:
*
* const styles = {
* border: {
* style: {
* top: 'solid'
* }
* }
* }
*
* as it is better to modify border style independently from other values. On the other part the output of the border might be
* desired as `border-top`, `border-left`, etc notation.
*
* In the above example a reducer should return a side border value that combines style, color and width:
*
* styleProcessor.setExtractor( 'border-top', styles => {
* return {
* color: styles.border.color.top,
* style: styles.border.style.top,
* width: styles.border.width.top
* }
* } );
*
* @param {String} name
* @param {Function|String} callbackOrPath Callback that return a requested value or path string for single values.
*/
setExtractor( name, callbackOrPath ) {
this._extractors.set( name, callbackOrPath );
}
/**
* Adds a reducer callback for a style property.
*
* Reducer returns a minimal notation for given style name. For longhand properties it is not required to write a reducer as
* by default the direct value from style path is taken.
*
* For shorthand styles a reducer should return minimal style notation either by returning single name-value tuple or multiple tuples
* if a shorthand cannot be used. For instance for a margin shorthand a reducer might return:
*
* const marginShortHandTuple = [
* [ 'margin', '1px 1px 2px' ]
* ];
*
* or a longhand tuples for defined values:
*
* // Considering margin.bottom and margin.left are undefined.
* const marginLonghandsTuples = [
* [ 'margin-top', '1px' ],
* [ 'margin-right', '1px' ]
* ];
*
* A reducer obtains a normalized style value:
*
* // Simplified reducer that always outputs 4 values which are always present:
* stylesProcessor.setReducer( 'margin', margin => {
* return [
* [ 'margin', `${ margin.top } ${ margin.right } ${ margin.bottom } ${ margin.left }` ]
* ]
* } );
*
* @param {String} name
* @param {Function} callback
*/
setReducer( name, callback ) {
this._reducers.set( name, callback );
}
/**
* Defines a style shorthand relation to other style notations.
*
* stylesProcessor.setStyleRelation( 'margin', [
* 'margin-top',
* 'margin-right',
* 'margin-bottom',
* 'margin-left'
* ] );
*
* This enables expanding of style names for shorthands. For instance, if defined,
* {@link module:engine/conversion/viewconsumable~ViewConsumable view consumable} items are automatically created
* for long-hand margin style notation alongside the `'margin'` item.
*
* This means that when an element being converted has a style `margin`, a converter for `margin-left` will work just
* fine since the view consumable will contain a consumable `margin-left` item (thanks to the relation) and
* `element.getStyle( 'margin-left' )` will work as well assuming that the style processor was correctly configured.
* However, once `margin-left` is consumed, `margin` will not be consumable anymore.
*
* @param {String} shorthandName
* @param {Array.<String>} styleNames
*/
setStyleRelation( shorthandName, styleNames ) {
this._mapStyleNames( shorthandName, styleNames );
for ( const alsoName of styleNames ) {
this._mapStyleNames( alsoName, [ shorthandName ] );
}
}
/**
* Set two-way binding of style names.
*
* @param {String} name
* @param {Array.<String>} styleNames
* @private
*/
_mapStyleNames( name, styleNames ) {
if ( !this._consumables.has( name ) ) {
this._consumables.set( name, [] );
}
this._consumables.get( name ).push( ...styleNames );
}
}
// Parses inline styles and puts property - value pairs into styles map.
//
// @param {String} stylesString Styles to parse.
// @returns {Map.<String, String>} stylesMap Map of parsed properties and values.
function parseInlineStyles( stylesString ) {
// `null` if no quote was found in input string or last found quote was a closing quote. See below.
let quoteType = null;
let propertyNameStart = 0;
let propertyValueStart = 0;
let propertyName = null;
const stylesMap = new Map();
// Do not set anything if input string is empty.
if ( stylesString === '' ) {
return stylesMap;
}
// Fix inline styles that do not end with `;` so they are compatible with algorithm below.
if ( stylesString.charAt( stylesString.length - 1 ) != ';' ) {
stylesString = stylesString + ';';
}
// Seek the whole string for "special characters".
for ( let i = 0; i < stylesString.length; i++ ) {
const char = stylesString.charAt( i );
if ( quoteType === null ) {
// No quote found yet or last found quote was a closing quote.
switch ( char ) {
case ':':
// Most of time colon means that property name just ended.
// Sometimes however `:` is found inside property value (for example in background image url).
if ( !propertyName ) {
// Treat this as end of property only if property name is not already saved.
// Save property name.
propertyName = stylesString.substr( propertyNameStart, i - propertyNameStart );
// Save this point as the start of property value.
propertyValueStart = i + 1;
}
break;
case '"':
case '\'':
// Opening quote found (this is an opening quote, because `quoteType` is `null`).
quoteType = char;
break;
case ';': {
// Property value just ended.
// Use previously stored property value start to obtain property value.
const propertyValue = stylesString.substr( propertyValueStart, i - propertyValueStart );
if ( propertyName ) {
// Save parsed part.
stylesMap.set( propertyName.trim(), propertyValue.trim() );
}
propertyName = null;
// Save this point as property name start. Property name starts immediately after previous property value ends.
propertyNameStart = i + 1;
break;
}
}
} else if ( char === quoteType ) {
// If a quote char is found and it is a closing quote, mark this fact by `null`-ing `quoteType`.
quoteType = null;
}
}
return stylesMap;
}
// Return lodash compatible path from style name.
function toPath( name ) {
return name.replace( '-', '.' );
}
// Appends style definition to the styles object.
//
// @param {String} nameOrPath
// @param {String|Object} valueOrObject
// @private
function appendStyleValue( stylesObject, nameOrPath, valueOrObject ) {
let valueToSet = valueOrObject;
if ( isObject( valueOrObject ) ) {
valueToSet = merge( {}, get( stylesObject, nameOrPath ), valueOrObject );
}
set( stylesObject, nameOrPath, valueToSet );
}
/**
* A CSS style property descriptor that contains tuplet of two strings:
*
* - first string describes property name
* - second string describes property value
*
* const marginDescriptor = [ 'margin', '2px 3em' ];
* const marginTopDescriptor = [ 'margin-top', '2px' ];
*
* @typedef {Array.<String, String>} module:engine/view/stylesmap~PropertyDescriptor
*/
/**
* An object describing values associated with the sides of a box, for instance margins, paddings,
* border widths, border colors, etc.
*
* const margin = {
* top: '1px',
* right: '3px',
* bottom: '3px',
* left: '7px'
* };
*
* const borderColor = {
* top: 'red',
* right: 'blue',
* bottom: 'blue',
* left: 'red'
* };
*
* @typedef {Object} module:engine/view/stylesmap~BoxSides
*
* @property {String} top Top side value.
* @property {String} right Right side value.
* @property {String} bottom Bottom side value.
* @property {String} left Left side value.
*/