src/third_party/closure_library/closure/goog/i18n/bidiformatter.js

// Copyright 2009 The Closure Library Authors. All Rights Reserved.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//      http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS-IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

/**
 * @fileoverview Utility for formatting text for display in a potentially
 * opposite-directionality context without garbling.
 * Mostly a port of http://go/formatter.cc.
 */


goog.provide('goog.i18n.BidiFormatter');

goog.require('goog.html.SafeHtml');
goog.require('goog.html.legacyconversions');
goog.require('goog.i18n.bidi');
goog.require('goog.i18n.bidi.Dir');
goog.require('goog.i18n.bidi.Format');



/**
 * Utility class for formatting text for display in a potentially
 * opposite-directionality context without garbling. Provides the following
 * functionality:
 *
 * 1. BiDi Wrapping
 * When text in one language is mixed into a document in another, opposite-
 * directionality language, e.g. when an English business name is embedded in a
 * Hebrew web page, both the inserted string and the text following it may be
 * displayed incorrectly unless the inserted string is explicitly separated
 * from the surrounding text in a "wrapper" that declares its directionality at
 * the start and then resets it back at the end. This wrapping can be done in
 * HTML mark-up (e.g. a 'span dir="rtl"' tag) or - only in contexts where
 * mark-up can not be used - in Unicode BiDi formatting codes (LRE|RLE and PDF).
 * Providing such wrapping services is the basic purpose of the BiDi formatter.
 *
 * 2. Directionality estimation
 * How does one know whether a string about to be inserted into surrounding
 * text has the same directionality? Well, in many cases, one knows that this
 * must be the case when writing the code doing the insertion, e.g. when a
 * localized message is inserted into a localized page. In such cases there is
 * no need to involve the BiDi formatter at all. In the remaining cases, e.g.
 * when the string is user-entered or comes from a database, the language of
 * the string (and thus its directionality) is not known a priori, and must be
 * estimated at run-time. The BiDi formatter does this automatically.
 *
 * 3. Escaping
 * When wrapping plain text - i.e. text that is not already HTML or HTML-
 * escaped - in HTML mark-up, the text must first be HTML-escaped to prevent XSS
 * attacks and other nasty business. This of course is always true, but the
 * escaping can not be done after the string has already been wrapped in
 * mark-up, so the BiDi formatter also serves as a last chance and includes
 * escaping services.
 *
 * Thus, in a single call, the formatter will escape the input string as
 * specified, determine its directionality, and wrap it as necessary. It is
 * then up to the caller to insert the return value in the output.
 *
 * See http://wiki/Main/TemplatesAndBiDi for more information.
 *
 * @param {goog.i18n.bidi.Dir|number|boolean|null} contextDir The context
 *     directionality, in one of the following formats:
 *     1. A goog.i18n.bidi.Dir constant. NEUTRAL is treated the same as null,
 *        i.e. unknown, for backward compatibility with legacy calls.
 *     2. A number (positive = LTR, negative = RTL, 0 = unknown).
 *     3. A boolean (true = RTL, false = LTR).
 *     4. A null for unknown directionality.
 * @param {boolean=} opt_alwaysSpan Whether {@link #spanWrap} should always
 *     use a 'span' tag, even when the input directionality is neutral or
 *     matches the context, so that the DOM structure of the output does not
 *     depend on the combination of directionalities. Default: false.
 * @constructor
 * @final
 */
goog.i18n.BidiFormatter = function(contextDir, opt_alwaysSpan) {
  /**
   * The overall directionality of the context in which the formatter is being
   * used.
   * @type {?goog.i18n.bidi.Dir}
   * @private
   */
  this.contextDir_ = goog.i18n.bidi.toDir(contextDir, true /* opt_noNeutral */);

  /**
   * Whether {@link #spanWrap} and similar methods should always use the same
   * span structure, regardless of the combination of directionalities, for a
   * stable DOM structure.
   * @type {boolean}
   * @private
   */
  this.alwaysSpan_ = !!opt_alwaysSpan;
};


/**
 * @return {?goog.i18n.bidi.Dir} The context directionality.
 */
goog.i18n.BidiFormatter.prototype.getContextDir = function() {
  return this.contextDir_;
};


/**
 * @return {boolean} Whether alwaysSpan is set.
 */
goog.i18n.BidiFormatter.prototype.getAlwaysSpan = function() {
  return this.alwaysSpan_;
};


/**
 * @param {goog.i18n.bidi.Dir|number|boolean|null} contextDir The context
 *     directionality, in one of the following formats:
 *     1. A goog.i18n.bidi.Dir constant. NEUTRAL is treated the same as null,
 *        i.e. unknown.
 *     2. A number (positive = LTR, negative = RTL, 0 = unknown).
 *     3. A boolean (true = RTL, false = LTR).
 *     4. A null for unknown directionality.
 */
goog.i18n.BidiFormatter.prototype.setContextDir = function(contextDir) {
  this.contextDir_ = goog.i18n.bidi.toDir(contextDir, true /* opt_noNeutral */);
};


/**
 * @param {boolean} alwaysSpan Whether {@link #spanWrap} should always use a
 *     'span' tag, even when the input directionality is neutral or matches the
 *     context, so that the DOM structure of the output does not depend on the
 *     combination of directionalities.
 */
goog.i18n.BidiFormatter.prototype.setAlwaysSpan = function(alwaysSpan) {
  this.alwaysSpan_ = alwaysSpan;
};


/**
 * Returns the directionality of input argument {@code str}.
 * Identical to {@link goog.i18n.bidi.estimateDirection}.
 *
 * @param {string} str The input text.
 * @param {boolean=} opt_isHtml Whether {@code str} is HTML / HTML-escaped.
 *     Default: false.
 * @return {goog.i18n.bidi.Dir} Estimated overall directionality of {@code str}.
 */
goog.i18n.BidiFormatter.prototype.estimateDirection =
    goog.i18n.bidi.estimateDirection;


/**
 * Returns true if two given directionalities are opposite.
 * Note: the implementation is based on the numeric values of the Dir enum.
 *
 * @param {?goog.i18n.bidi.Dir} dir1 1st directionality.
 * @param {?goog.i18n.bidi.Dir} dir2 2nd directionality.
 * @return {boolean} Whether the directionalities are opposite.
 * @private
 */
goog.i18n.BidiFormatter.prototype.areDirectionalitiesOpposite_ = function(dir1,
    dir2) {
  return dir1 * dir2 < 0;
};


/**
 * Returns a unicode BiDi mark matching the context directionality (LRM or
 * RLM) if {@code opt_dirReset}, and if either the directionality or the exit
 * directionality of {@code str} is opposite to the context directionality.
 * Otherwise returns the empty string.
 *
 * @param {string} str The input text.
 * @param {goog.i18n.bidi.Dir} dir {@code str}'s overall directionality.
 * @param {boolean=} opt_isHtml Whether {@code str} is HTML / HTML-escaped.
 *     Default: false.
 * @param {boolean=} opt_dirReset Whether to perform the reset. Default: false.
 * @return {string} A unicode BiDi mark or the empty string.
 * @private
 */
goog.i18n.BidiFormatter.prototype.dirResetIfNeeded_ = function(str, dir,
    opt_isHtml, opt_dirReset) {
  // endsWithRtl and endsWithLtr are called only if needed (short-circuit).
  if (opt_dirReset &&
      (this.areDirectionalitiesOpposite_(dir, this.contextDir_) ||
       (this.contextDir_ == goog.i18n.bidi.Dir.LTR &&
        goog.i18n.bidi.endsWithRtl(str, opt_isHtml)) ||
       (this.contextDir_ == goog.i18n.bidi.Dir.RTL &&
        goog.i18n.bidi.endsWithLtr(str, opt_isHtml)))) {
    return this.contextDir_ == goog.i18n.bidi.Dir.LTR ?
        goog.i18n.bidi.Format.LRM : goog.i18n.bidi.Format.RLM;
  } else {
    return '';
  }
};


/**
 * Returns "rtl" if {@code str}'s estimated directionality is RTL, and "ltr" if
 * it is LTR. In case it's NEUTRAL, returns "rtl" if the context directionality
 * is RTL, and "ltr" otherwise.
 * Needed for GXP, which can't handle dirAttr.
 * Example use case:
 * &lt;td expr:dir='bidiFormatter.dirAttrValue(foo)'&gt;
 *   &lt;gxp:eval expr='foo'&gt;
 * &lt;/td&gt;
 *
 * @param {string} str Text whose directionality is to be estimated.
 * @param {boolean=} opt_isHtml Whether {@code str} is HTML / HTML-escaped.
 *     Default: false.
 * @return {string} "rtl" or "ltr", according to the logic described above.
 */
goog.i18n.BidiFormatter.prototype.dirAttrValue = function(str, opt_isHtml) {
  return this.knownDirAttrValue(this.estimateDirection(str, opt_isHtml));
};


/**
 * Returns "rtl" if the given directionality is RTL, and "ltr" if it is LTR. In
 * case it's NEUTRAL, returns "rtl" if the context directionality is RTL, and
 * "ltr" otherwise.
 *
 * @param {goog.i18n.bidi.Dir} dir A directionality.
 * @return {string} "rtl" or "ltr", according to the logic described above.
 */
goog.i18n.BidiFormatter.prototype.knownDirAttrValue = function(dir) {
  var resolvedDir = dir == goog.i18n.bidi.Dir.NEUTRAL ? this.contextDir_ : dir;
  return resolvedDir == goog.i18n.bidi.Dir.RTL ? 'rtl' : 'ltr';
};


/**
 * Returns 'dir="ltr"' or 'dir="rtl"', depending on {@code str}'s estimated
 * directionality, if it is not the same as the context directionality.
 * Otherwise, returns the empty string.
 *
 * @param {string} str Text whose directionality is to be estimated.
 * @param {boolean=} opt_isHtml Whether {@code str} is HTML / HTML-escaped.
 *     Default: false.
 * @return {string} 'dir="rtl"' for RTL text in non-RTL context; 'dir="ltr"' for
 *     LTR text in non-LTR context; else, the empty string.
 */
goog.i18n.BidiFormatter.prototype.dirAttr = function(str, opt_isHtml) {
  return this.knownDirAttr(this.estimateDirection(str, opt_isHtml));
};


/**
 * Returns 'dir="ltr"' or 'dir="rtl"', depending on the given directionality, if
 * it is not the same as the context directionality. Otherwise, returns the
 * empty string.
 *
 * @param {goog.i18n.bidi.Dir} dir A directionality.
 * @return {string} 'dir="rtl"' for RTL text in non-RTL context; 'dir="ltr"' for
 *     LTR text in non-LTR context; else, the empty string.
 */
goog.i18n.BidiFormatter.prototype.knownDirAttr = function(dir) {
  if (dir != this.contextDir_) {
    return dir == goog.i18n.bidi.Dir.RTL ? 'dir="rtl"' :
        dir == goog.i18n.bidi.Dir.LTR ? 'dir="ltr"' : '';
  }
  return '';
};


/**
 * Formats a string of unknown directionality for use in HTML output of the
 * context directionality, so an opposite-directionality string is neither
 * garbled nor garbles what follows it.
 * The algorithm: estimates the directionality of input argument {@code html}.
 * In case its directionality doesn't match the context directionality, wraps it
 * with a 'span' tag and adds a "dir" attribute (either 'dir="rtl"' or
 * 'dir="ltr"'). If setAlwaysSpan(true) was used, the input is always wrapped
 * with 'span', skipping just the dir attribute when it's not needed.
 *
 * If {@code opt_dirReset}, and if the overall directionality or the exit
 * directionality of {@code str} are opposite to the context directionality, a
 * trailing unicode BiDi mark matching the context directionality is appened
 * (LRM or RLM).
 *
 * @param {!goog.html.SafeHtml} html The input HTML.
 * @param {boolean=} opt_dirReset Whether to append a trailing unicode bidi mark
 *     matching the context directionality, when needed, to prevent the possible
 *     garbling of whatever may follow {@code html}. Default: true.
 * @return {!goog.html.SafeHtml} Input text after applying the processing.
 */
goog.i18n.BidiFormatter.prototype.spanWrapSafeHtml = function(html,
    opt_dirReset) {
  return this.spanWrapSafeHtmlWithKnownDir(null, html, opt_dirReset);
};


/**
 * String version of {@link #spanWrapSafeHtml}.
 *
 * If !{@code opt_isHtml}, HTML-escapes {@code str} regardless of wrapping.
 *
 * @param {string} str The input text.
 * @param {boolean=} opt_isHtml Whether {@code str} is HTML / HTML-escaped.
 *     Default: false.
 * @param {boolean=} opt_dirReset Whether to append a trailing unicode bidi mark
 *     matching the context directionality, when needed, to prevent the possible
 *     garbling of whatever may follow {@code str}. Default: true.
 * @return {string} Input text after applying the above processing.
 */
goog.i18n.BidiFormatter.prototype.spanWrap = function(str, opt_isHtml,
    opt_dirReset) {
  return this.spanWrapWithKnownDir(null, str, opt_isHtml, opt_dirReset);
};


/**
 * Formats a string of given directionality for use in HTML output of the
 * context directionality, so an opposite-directionality string is neither
 * garbled nor garbles what follows it.
 * The algorithm: If {@code dir} doesn't match the context directionality, wraps
 * {@code html} with a 'span' tag and adds a "dir" attribute (either 'dir="rtl"'
 * or 'dir="ltr"'). If setAlwaysSpan(true) was used, the input is always wrapped
 * with 'span', skipping just the dir attribute when it's not needed.
 *
 * If {@code opt_dirReset}, and if {@code dir} or the exit directionality of
 * {@code html} are opposite to the context directionality, a trailing unicode
 * BiDi mark matching the context directionality is appened (LRM or RLM).
 *
 * @param {?goog.i18n.bidi.Dir} dir {@code html}'s overall directionality, or
 *     null if unknown and needs to be estimated.
 * @param {!goog.html.SafeHtml} html The input HTML.
 * @param {boolean=} opt_dirReset Whether to append a trailing unicode bidi mark
 *     matching the context directionality, when needed, to prevent the possible
 *     garbling of whatever may follow {@code html}. Default: true.
 * @return {!goog.html.SafeHtml} Input text after applying the processing.
 */
goog.i18n.BidiFormatter.prototype.spanWrapSafeHtmlWithKnownDir = function(dir,
    html, opt_dirReset) {
  if (dir == null) {
    dir = this.estimateDirection(goog.html.SafeHtml.unwrap(html), true);
  }
  return this.spanWrapWithKnownDir_(dir, html, opt_dirReset);
};


/**
 * String version of {@link #spanWrapSafeHtmlWithKnownDir}.
 *
 * If !{@code opt_isHtml}, HTML-escapes {@code str} regardless of wrapping.
 *
 * @param {?goog.i18n.bidi.Dir} dir {@code str}'s overall directionality, or
 *     null if unknown and needs to be estimated.
 * @param {string} str The input text.
 * @param {boolean=} opt_isHtml Whether {@code str} is HTML / HTML-escaped.
 *     Default: false.
 * @param {boolean=} opt_dirReset Whether to append a trailing unicode bidi mark
 *     matching the context directionality, when needed, to prevent the possible
 *     garbling of whatever may follow {@code str}. Default: true.
 * @return {string} Input text after applying the above processing.
 */
goog.i18n.BidiFormatter.prototype.spanWrapWithKnownDir = function(dir, str,
    opt_isHtml, opt_dirReset) {
  // We're calling legacy conversions, but quickly unwrapping it.
  var html = opt_isHtml ? goog.html.legacyconversions.safeHtmlFromString(str) :
      goog.html.SafeHtml.htmlEscape(str);
  return goog.html.SafeHtml.unwrap(
      this.spanWrapSafeHtmlWithKnownDir(dir, html, opt_dirReset));
};


/**
 * The internal implementation of spanWrapSafeHtmlWithKnownDir for non-null dir,
 * to help the compiler optimize.
 *
 * @param {goog.i18n.bidi.Dir} dir {@code str}'s overall directionality.
 * @param {!goog.html.SafeHtml} html The input HTML.
 * @param {boolean=} opt_dirReset Whether to append a trailing unicode bidi mark
 *     matching the context directionality, when needed, to prevent the possible
 *     garbling of whatever may follow {@code str}. Default: true.
 * @return {!goog.html.SafeHtml} Input text after applying the above processing.
 * @private
 */
goog.i18n.BidiFormatter.prototype.spanWrapWithKnownDir_ = function(dir, html,
    opt_dirReset) {
  opt_dirReset = opt_dirReset || (opt_dirReset == undefined);

  var result;
  // Whether to add the "dir" attribute.
  var dirCondition =
      dir != goog.i18n.bidi.Dir.NEUTRAL && dir != this.contextDir_;
  if (this.alwaysSpan_ || dirCondition) {  // Wrap is needed
    var dirAttribute;
    if (dirCondition) {
      dirAttribute = dir == goog.i18n.bidi.Dir.RTL ? 'rtl' : 'ltr';
    }
    result = goog.html.SafeHtml.create('span', {'dir': dirAttribute}, html);
  } else {
    result = html;
  }
  var str = goog.html.SafeHtml.unwrap(html);
  result = goog.html.SafeHtml.concatWithDir(goog.i18n.bidi.Dir.NEUTRAL, result,
      this.dirResetIfNeeded_(str, dir, true, opt_dirReset));
  return result;
};


/**
 * Formats a string of unknown directionality for use in plain-text output of
 * the context directionality, so an opposite-directionality string is neither
 * garbled nor garbles what follows it.
 * As opposed to {@link #spanWrap}, this makes use of unicode BiDi formatting
 * characters. In HTML, its *only* valid use is inside of elements that do not
 * allow mark-up, e.g. an 'option' tag.
 * The algorithm: estimates the directionality of input argument {@code str}.
 * In case it doesn't match  the context directionality, wraps it with Unicode
 * BiDi formatting characters: RLE{@code str}PDF for RTL text, and
 * LRE{@code str}PDF for LTR text.
 *
 * If {@code opt_dirReset}, and if the overall directionality or the exit
 * directionality of {@code str} are opposite to the context directionality, a
 * trailing unicode BiDi mark matching the context directionality is appended
 * (LRM or RLM).
 *
 * Does *not* do HTML-escaping regardless of the value of {@code opt_isHtml}.
 * The return value can be HTML-escaped as necessary.
 *
 * @param {string} str The input text.
 * @param {boolean=} opt_isHtml Whether {@code str} is HTML / HTML-escaped.
 *     Default: false.
 * @param {boolean=} opt_dirReset Whether to append a trailing unicode bidi mark
 *     matching the context directionality, when needed, to prevent the possible
 *     garbling of whatever may follow {@code str}. Default: true.
 * @return {string} Input text after applying the above processing.
 */
goog.i18n.BidiFormatter.prototype.unicodeWrap = function(str, opt_isHtml,
    opt_dirReset) {
  return this.unicodeWrapWithKnownDir(null, str, opt_isHtml, opt_dirReset);
};


/**
 * Formats a string of given directionality for use in plain-text output of the
 * context directionality, so an opposite-directionality string is neither
 * garbled nor garbles what follows it.
 * As opposed to {@link #spanWrapWithKnownDir}, makes use of unicode BiDi
 * formatting characters. In HTML, its *only* valid use is inside of elements
 * that do not allow mark-up, e.g. an 'option' tag.
 * The algorithm: If {@code dir} doesn't match the context directionality, wraps
 * {@code str} with Unicode BiDi formatting characters: RLE{@code str}PDF for
 * RTL text, and LRE{@code str}PDF for LTR text.
 *
 * If {@code opt_dirReset}, and if the overall directionality or the exit
 * directionality of {@code str} are opposite to the context directionality, a
 * trailing unicode BiDi mark matching the context directionality is appended
 * (LRM or RLM).
 *
 * Does *not* do HTML-escaping regardless of the value of {@code opt_isHtml}.
 * The return value can be HTML-escaped as necessary.
 *
 * @param {?goog.i18n.bidi.Dir} dir {@code str}'s overall directionality, or
 *     null if unknown and needs to be estimated.
 * @param {string} str The input text.
 * @param {boolean=} opt_isHtml Whether {@code str} is HTML / HTML-escaped.
 *     Default: false.
 * @param {boolean=} opt_dirReset Whether to append a trailing unicode bidi mark
 *     matching the context directionality, when needed, to prevent the possible
 *     garbling of whatever may follow {@code str}. Default: true.
 * @return {string} Input text after applying the above processing.
 */
goog.i18n.BidiFormatter.prototype.unicodeWrapWithKnownDir = function(dir, str,
    opt_isHtml, opt_dirReset) {
  if (dir == null) {
    dir = this.estimateDirection(str, opt_isHtml);
  }
  return this.unicodeWrapWithKnownDir_(dir, str, opt_isHtml, opt_dirReset);
};


/**
 * The internal implementation of unicodeWrapWithKnownDir for non-null dir, to
 * help the compiler optimize.
 *
 * @param {goog.i18n.bidi.Dir} dir {@code str}'s overall directionality.
 * @param {string} str The input text.
 * @param {boolean=} opt_isHtml Whether {@code str} is HTML / HTML-escaped.
 *     Default: false.
 * @param {boolean=} opt_dirReset Whether to append a trailing unicode bidi mark
 *     matching the context directionality, when needed, to prevent the possible
 *     garbling of whatever may follow {@code str}. Default: true.
 * @return {string} Input text after applying the above processing.
 * @private
 */
goog.i18n.BidiFormatter.prototype.unicodeWrapWithKnownDir_ = function(dir, str,
    opt_isHtml, opt_dirReset) {
  opt_dirReset = opt_dirReset || (opt_dirReset == undefined);
  var result = [];
  if (dir != goog.i18n.bidi.Dir.NEUTRAL && dir != this.contextDir_) {
    result.push(dir == goog.i18n.bidi.Dir.RTL ? goog.i18n.bidi.Format.RLE :
                                                goog.i18n.bidi.Format.LRE);
    result.push(str);
    result.push(goog.i18n.bidi.Format.PDF);
  } else {
    result.push(str);
  }

  result.push(this.dirResetIfNeeded_(str, dir, opt_isHtml, opt_dirReset));
  return result.join('');
};


/**
 * Returns a Unicode BiDi mark matching the context directionality (LRM or RLM)
 * if the directionality or the exit directionality of {@code str} are opposite
 * to the context directionality. Otherwise returns the empty string.
 *
 * @param {string} str The input text.
 * @param {boolean=} opt_isHtml Whether {@code str} is HTML / HTML-escaped.
 *     Default: false.
 * @return {string} A Unicode bidi mark matching the global directionality or
 *     the empty string.
 */
goog.i18n.BidiFormatter.prototype.markAfter = function(str, opt_isHtml) {
  return this.markAfterKnownDir(null, str, opt_isHtml);
};


/**
 * Returns a Unicode BiDi mark matching the context directionality (LRM or RLM)
 * if the given directionality or the exit directionality of {@code str} are
 * opposite to the context directionality. Otherwise returns the empty string.
 *
 * @param {?goog.i18n.bidi.Dir} dir {@code str}'s overall directionality, or
 *     null if unknown and needs to be estimated.
 * @param {string} str The input text.
 * @param {boolean=} opt_isHtml Whether {@code str} is HTML / HTML-escaped.
 *     Default: false.
 * @return {string} A Unicode bidi mark matching the global directionality or
 *     the empty string.
 */
goog.i18n.BidiFormatter.prototype.markAfterKnownDir = function(
    dir, str, opt_isHtml) {
  if (dir == null) {
    dir = this.estimateDirection(str, opt_isHtml);
  }
  return this.dirResetIfNeeded_(str, dir, opt_isHtml, true);
};


/**
 * Returns the Unicode BiDi mark matching the context directionality (LRM for
 * LTR context directionality, RLM for RTL context directionality), or the
 * empty string for neutral / unknown context directionality.
 *
 * @return {string} LRM for LTR context directionality and RLM for RTL context
 *     directionality.
 */
goog.i18n.BidiFormatter.prototype.mark = function() {
  switch (this.contextDir_) {
    case (goog.i18n.bidi.Dir.LTR):
      return goog.i18n.bidi.Format.LRM;
    case (goog.i18n.bidi.Dir.RTL):
      return goog.i18n.bidi.Format.RLM;
    default:
      return '';
  }
};


/**
 * Returns 'right' for RTL context directionality. Otherwise (LTR or neutral /
 * unknown context directionality) returns 'left'.
 *
 * @return {string} 'right' for RTL context directionality and 'left' for other
 *     context directionality.
 */
goog.i18n.BidiFormatter.prototype.startEdge = function() {
  return this.contextDir_ == goog.i18n.bidi.Dir.RTL ?
      goog.i18n.bidi.RIGHT : goog.i18n.bidi.LEFT;
};


/**
 * Returns 'left' for RTL context directionality. Otherwise (LTR or neutral /
 * unknown context directionality) returns 'right'.
 *
 * @return {string} 'left' for RTL context directionality and 'right' for other
 *     context directionality.
 */
goog.i18n.BidiFormatter.prototype.endEdge = function() {
  return this.contextDir_ == goog.i18n.bidi.Dir.RTL ?
      goog.i18n.bidi.LEFT : goog.i18n.bidi.RIGHT;
};