Get rid of BidiUtils as a class holding only static methods. I was reminded by

lib/i18n/bidi_utils.dart

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 /**
  * Bidi stands for Bi-directional text.
  * According to http://en.wikipedia.org/wiki/Bi-directional_text:
  * Bi-directional text is text containing text in both text directionalities,
  * both right-to-left (RTL) and left-to-right (LTR). It generally involves text
  * containing different types of alphabets, but may also refer to boustrophedon,
@@ skipping 30 matching lines @@
   
   /**
    * Returns true if [otherDirection] is known to be different from this
    * direction.
    */
   bool isDirectionChange(TextDirection otherDirection) {
     return otherDirection != TextDirection.UNKNOWN && this != otherDirection;
   }
 }
 
-class BidiUtils {
-  /** Unicode "Left-To-Right Embedding" (LRE) character. */
-  static final LRE = '\u202A';
-
-  /** Unicode "Right-To-Left Embedding" (RLE) character. */
-  static final RLE = '\u202B';
-
-  /** Unicode "Pop Directional Formatting" (PDF) character. */
-  static final PDF = '\u202C';
-
-  /** Unicode "Left-To-Right Mark" (LRM) character. */
-  static final LRM = '\u200E';
-
-  /** Unicode "Right-To-Left Mark" (RLM) character. */
-  static final RLM = '\u200F';
-
-  /** Constant to define the threshold of RTL directionality. */
-  static num _RTL_DETECTION_THRESHOLD = 0.40;
-
-  /**
-   * Practical patterns to identify strong LTR and RTL characters, respectively.
-   * These patterns are not completely correct according to the Unicode
-   * standard. They are simplified for performance and small code size.
-   */
-  static final String _LTR_CHARS =
-      @'A-Za-z\u00C0-\u00D6\u00D8-\u00F6\u00F8-\u02B8\u0300-\u0590'
-      @'\u0800-\u1FFF\u2C00-\uFB1C\uFDFE-\uFE6F\uFEFD-\uFFFF';
-  static final String _RTL_CHARS = @'\u0591-\u07FF\uFB1D-\uFDFD\uFE70-\uFEFC';
-
-  /**
-   * Returns the input [text] with spaces instead of HTML tags or HTML escapes,
-   * which is helpful for text directionality estimation.
-   * Note: This function should not be used in other contexts.
-   * It does not deal well with many things: comments, script,
-   * elements, style elements, dir attribute,`>` in quoted attribute values,
-   * etc. But it does handle well enough the most common use cases.
-   * Since the worst that can happen as a result of these shortcomings is that
-   * the wrong directionality will be estimated, we have not invested in
-   * improving this.
-   */
-  static String stripHtmlIfNeeded(String text) {
-    // The regular expression is simplified for an HTML tag (opening or 
-    // closing) or an HTML escape. We might want to skip over such expressions
-    // when estimating the text directionality.
-    return text.replaceAll(const RegExp(@'<[^>]*>|&[^;]+;'), ' ');
-  }
-
-  /**
-   * Determines if the first character in [text] with strong directionality is
-   * LTR. If [isHtml] is true, the text is HTML or HTML-escaped.
-   */
-  static bool startsWithLtr(String text, [isHtml=false]) {
-    return const RegExp('^[^$_RTL_CHARS]*[$_LTR_CHARS]').hasMatch(
-        isHtml? stripHtmlIfNeeded(text) : text);
-  }
-
-  /**
-   * Determines if the first character in [text] with strong directionality is
-   * RTL. If [isHtml] is true, the text is HTML or HTML-escaped.
-   */
-  static bool startsWithRtl(String text, [isHtml=false]) {
-    return const RegExp('^[^$_LTR_CHARS]*[$_RTL_CHARS]').hasMatch(
-        isHtml? stripHtmlIfNeeded(text) : text);
-  }
-
-  /**
-   * Determines if the exit directionality (ie, the last strongly-directional
-   * character in [text] is LTR. If [isHtml] is true, the text is HTML or
-   * HTML-escaped.
-   */
-  static bool endsWithLtr(String text, [isHtml=false]) {
-    return const RegExp('[$_LTR_CHARS][^$_RTL_CHARS]*\$').hasMatch(
-        isHtml? stripHtmlIfNeeded(text) : text);
-  }
-
-  /**
-   * Determines if the exit directionality (ie, the last strongly-directional
-   * character in [text] is RTL. If [isHtml] is true, the text is HTML or
-   * HTML-escaped.
-   */
-  static bool endsWithRtl(String text, [isHtml=false]) {
-    return const RegExp('[$_RTL_CHARS][^$_LTR_CHARS]*\$').hasMatch(
-        isHtml? stripHtmlIfNeeded(text) : text);
-  }
-
-  /**
-   * Determines if the given [text] has any LTR characters in it.
-   * If [isHtml] is true, the text is HTML or HTML-escaped.
-   */
-  static bool hasAnyLtr(String text, [isHtml=false]) {
-    return const RegExp(@'[' '$_LTR_CHARS' @']').hasMatch(
-        isHtml? stripHtmlIfNeeded(text) : text);
-  }
-
-  /**
-   * Determines if the given [text] has any RTL characters in it.
-   * If [isHtml] is true, the text is HTML or HTML-escaped.
-   */
-  static bool hasAnyRtl(String text, [isHtml=false]) {
-    return const RegExp(@'[' '$_RTL_CHARS' @']').hasMatch(
-        isHtml? stripHtmlIfNeeded(text) : text);
-  }
-
-  /**
-   * Check if a BCP 47 / III [languageString] indicates an RTL language.
-   *
-   * i.e. either:
-   * - a language code explicitly specifying one of the right-to-left scripts,
-   *   e.g. "az-Arab", or
-   * - a language code specifying one of the languages normally written in a
-   *   right-to-left script, e.g. "fa" (Farsi), except ones explicitly
-   *   specifying Latin or Cyrillic script (which are the usual LTR
-   *   alternatives).
-   *
-   * The list of right-to-left scripts appears in the 100-199 range in
-   * http://www.unicode.org/iso15924/iso15924-num.html, of which Arabic and
-   * Hebrew are by far the most widely used. We also recognize Thaana, N'Ko, and
-   * Tifinagh, which also have significant modern usage. The rest (Syriac,
-   * Samaritan, Mandaic, etc.) seem to have extremely limited or no modern usage
-   * and are not recognized.
-   * The languages usually written in a right-to-left script are taken as those
-   * with Suppress-Script: Hebr|Arab|Thaa|Nkoo|Tfng  in
-   * http://www.iana.org/assignments/language-subtag-registry,
-   * as well as Sindhi (sd) and Uyghur (ug).
-   * The presence of other subtags of the language code, e.g. regions like EG
-   * (Egypt), is ignored.
-   */
-  static bool isRtlLanguage(String languageString) {
-    return const RegExp(@'^(ar|dv|he|iw|fa|nqo|ps|sd|ug|ur|yi|.*[-_]'
-        @'(Arab|Hebr|Thaa|Nkoo|Tfng))(?!.*[-_](Latn|Cyrl)($|-|_))'
-        @'($|-|_)', ignoreCase : true).hasMatch(languageString);
-  }
-
-  /**
-   * Enforce the [html] snippet in RTL directionality regardless of overall
-   * context. If the html piece was enclosed by a tag, the direction will be 
-   * applied to existing tag, otherwise a span tag will be added as wrapper.
-   * For this reason, if html snippet start with with tag, this tag must enclose
-   * the whole piece. If the tag already has a direction specified, this new one
-   * will override existing one in behavior (should work on Chrome, FF, and IE
-   * since this was ported directly from the Closure version).
-   */
-  static String enforceRtlInHtml(String html) {
-    return _enforceInHtmlHelper(html, 'rtl');
-  }
-
-  /**
-   * Enforce RTL on both end of the given [text] using unicode BiDi formatting
-   * characters RLE and PDF.
-   */
-  static String enforceRtlInText(String text) {
-    return '$RLE$text$PDF';
-  }
-
-  /**
-   * Enforce the [html] snippet in LTR directionality regardless of overall
-   * context. If the html piece was enclosed by a tag, the direction will be 
-   * applied to existing tag, otherwise a span tag will be added as wrapper.
-   * For this reason, if html snippet start with with tag, this tag must enclose
-   * the whole piece. If the tag already has a direction specified, this new one
-   * will override existing one in behavior (tested on FF and IE).
-   */
-  static String enforceLtrInHtml(String html) {
-    return _enforceInHtmlHelper(html, 'ltr');
-  }
-
-  /**
-   * Enforce LTR on both end of the given [text] using unicode BiDi formatting
-   * characters LRE and PDF.
-   */
-  static String enforceLtrInText(String text) {
-    return '$LRE$text$PDF';
-  }
-
-  /**
-   * Enforce the [html] snippet in the desired [direction] regardless of overall
-   * context. If the html piece was enclosed by a tag, the direction will be 
-   * applied to existing tag, otherwise a span tag will be added as wrapper.
-   * For this reason, if html snippet start with with tag, this tag must enclose
-   * the whole piece. If the tag already has a direction specified, this new one
-   * will override existing one in behavior (tested on FF and IE).
-   */
-  static String _enforceInHtmlHelper(String html, String direction) {
-    if (html.startsWith('<')) {
-      StringBuffer buffer = new StringBuffer();
-      var startIndex = 0;
-      Match match = const RegExp('<\\w+').firstMatch(html);
-      if (match != null) {
-        buffer.add(html.substring(
-            startIndex, match.end())).add(' dir=$direction');
-        startIndex = match.end();
-      }
-      return buffer.add(html.substring(startIndex)).toString();
-    }
-    // '\n' is important for FF so that it won't incorrectly merge span groups.
-    return '\n<span dir=$direction>$html</span>';
-  }
-
-  /**
-   * Apply bracket guard to [str] using html span tag. This is to address the 
-   * problem of messy bracket display that frequently happens in RTL layout.
-   * If [isRtlContext] is true, then we explicitly want to wrap in a span of RTL
-   * directionality, regardless of the estimated directionality.
-   */
-  static String guardBracketInHtml(String str, [bool isRtlContext]) {
-    var useRtl = isRtlContext == null ? hasAnyRtl(str) : isRtlContext;
-    RegExp matchingBrackets = 
-        const RegExp(@'(\(.*?\)+)|(\[.*?\]+)|(\{.*?\}+)|(&lt;.*?(&gt;)+)');
-    return _guardBracketHelper(str, matchingBrackets,
-        '<span dir=${useRtl? "rtl" : "ltr"}>', '</span>');
-  }
-
-  /**
-   * Apply bracket guard to [str] using LRM and RLM. This is to address the 
-   * problem of messy bracket display that frequently happens in RTL layout.
-   * This version works for both plain text and html, but in some cases is not
-   * as good as guardBracketInHtml.
-   * If [isRtlContext] is true, then we explicitly want to wrap in a span of RTL
-   * directionality, regardless of the estimated directionality.
-   */
-  static String guardBracketInText(String str, [bool isRtlContext]) {
-    var useRtl = isRtlContext == null ? hasAnyRtl(str) : isRtlContext;
-    var mark = useRtl ? RLM : LRM;
-    return _guardBracketHelper(str,
-        const RegExp(@'(\(.*?\)+)|(\[.*?\]+)|(\{.*?\}+)|(<.*?>+)'), mark, mark);
-  }
-
-  /**
-   * (Mostly) reimplements the $& functionality of "replace" in JavaScript.
-   * Given a [str] and the [regexp] to match with, optionally supply a string to
-   * be inserted [before] the match and/or [after]. For example, 
-   * `_guardBracketHelper('firetruck', const RegExp('truck'), 'hydrant', '!')`
-   * would return 'firehydrant!'.
-   */
-  // TODO(efortuna): Get rid of this once this is implemented in Dart.
-  // See Issue 2979.
-  static String _guardBracketHelper(String str, RegExp regexp, [String before,
-      String after]) {
+/** Unicode "Left-To-Right Embedding" (LRE) character. */
+final LRE = '\u202A';
+
+/** Unicode "Right-To-Left Embedding" (RLE) character. */
+final RLE = '\u202B';
+
+/** Unicode "Pop Directional Formatting" (PDF) character. */
+final PDF = '\u202C';
+
+/** Unicode "Left-To-Right Mark" (LRM) character. */
+final LRM = '\u200E';
+
+/** Unicode "Right-To-Left Mark" (RLM) character. */
+final RLM = '\u200F';
+
+/** Constant to define the threshold of RTL directionality. */
+num _RTL_DETECTION_THRESHOLD = 0.40;
+
+/**
+ * Practical patterns to identify strong LTR and RTL characters, respectively.
+ * These patterns are not completely correct according to the Unicode
+ * standard. They are simplified for performance and small code size.
+ */
+final String _LTR_CHARS =
+    @'A-Za-z\u00C0-\u00D6\u00D8-\u00F6\u00F8-\u02B8\u0300-\u0590'
+    @'\u0800-\u1FFF\u2C00-\uFB1C\uFDFE-\uFE6F\uFEFD-\uFFFF';
+final String _RTL_CHARS = @'\u0591-\u07FF\uFB1D-\uFDFD\uFE70-\uFEFC';
+
+/**
+ * Returns the input [text] with spaces instead of HTML tags or HTML escapes,
+ * which is helpful for text directionality estimation.
+ * Note: This function should not be used in other contexts.
+ * It does not deal well with many things: comments, script,
+ * elements, style elements, dir attribute,`>` in quoted attribute values,
+ * etc. But it does handle well enough the most common use cases.
+ * Since the worst that can happen as a result of these shortcomings is that
+ * the wrong directionality will be estimated, we have not invested in
+ * improving this.
+ */
+String stripHtmlIfNeeded(String text) {
+  // The regular expression is simplified for an HTML tag (opening or 
+  // closing) or an HTML escape. We might want to skip over such expressions
+  // when estimating the text directionality.
+  return text.replaceAll(const RegExp(@'<[^>]*>|&[^;]+;'), ' ');
+}
+
+/**
+ * Determines if the first character in [text] with strong directionality is
+ * LTR. If [isHtml] is true, the text is HTML or HTML-escaped.
+ */
+bool startsWithLtr(String text, [isHtml=false]) {
+  return const RegExp('^[^$_RTL_CHARS]*[$_LTR_CHARS]').hasMatch(
+      isHtml? stripHtmlIfNeeded(text) : text);
+}
+
+/**
+ * Determines if the first character in [text] with strong directionality is
+ * RTL. If [isHtml] is true, the text is HTML or HTML-escaped.
+ */
+bool startsWithRtl(String text, [isHtml=false]) {
+  return const RegExp('^[^$_LTR_CHARS]*[$_RTL_CHARS]').hasMatch(
+      isHtml? stripHtmlIfNeeded(text) : text);
+}
+
+/**
+ * Determines if the exit directionality (ie, the last strongly-directional
+ * character in [text] is LTR. If [isHtml] is true, the text is HTML or
+ * HTML-escaped.
+ */
+bool endsWithLtr(String text, [isHtml=false]) {
+  return const RegExp('[$_LTR_CHARS][^$_RTL_CHARS]*\$').hasMatch(
+      isHtml? stripHtmlIfNeeded(text) : text);
+}
+
+/**
+ * Determines if the exit directionality (ie, the last strongly-directional
+ * character in [text] is RTL. If [isHtml] is true, the text is HTML or
+ * HTML-escaped.
+ */
+bool endsWithRtl(String text, [isHtml=false]) {
+  return const RegExp('[$_RTL_CHARS][^$_LTR_CHARS]*\$').hasMatch(
+      isHtml? stripHtmlIfNeeded(text) : text);
+}
+
+/**
+ * Determines if the given [text] has any LTR characters in it.
+ * If [isHtml] is true, the text is HTML or HTML-escaped.
+ */
+bool hasAnyLtr(String text, [isHtml=false]) {
+  return const RegExp(@'[' '$_LTR_CHARS' @']').hasMatch(
+      isHtml? stripHtmlIfNeeded(text) : text);
+}
+
+/**
+ * Determines if the given [text] has any RTL characters in it.
+ * If [isHtml] is true, the text is HTML or HTML-escaped.
+ */
+bool hasAnyRtl(String text, [isHtml=false]) {
+  return const RegExp(@'[' '$_RTL_CHARS' @']').hasMatch(
+      isHtml? stripHtmlIfNeeded(text) : text);
+}
+
+/**
+ * Check if a BCP 47 / III [languageString] indicates an RTL language.
+ *
+ * i.e. either:
+ * - a language code explicitly specifying one of the right-to-left scripts,
+ *   e.g. "az-Arab", or
+ * - a language code specifying one of the languages normally written in a
+ *   right-to-left script, e.g. "fa" (Farsi), except ones explicitly
+ *   specifying Latin or Cyrillic script (which are the usual LTR
+ *   alternatives).
+ *
+ * The list of right-to-left scripts appears in the 100-199 range in
+ * http://www.unicode.org/iso15924/iso15924-num.html, of which Arabic and
+ * Hebrew are by far the most widely used. We also recognize Thaana, N'Ko, and
+ * Tifinagh, which also have significant modern usage. The rest (Syriac,
+ * Samaritan, Mandaic, etc.) seem to have extremely limited or no modern usage
+ * and are not recognized.
+ * The languages usually written in a right-to-left script are taken as those
+ * with Suppress-Script: Hebr|Arab|Thaa|Nkoo|Tfng  in
+ * http://www.iana.org/assignments/language-subtag-registry,
+ * as well as Sindhi (sd) and Uyghur (ug).
+ * The presence of other subtags of the language code, e.g. regions like EG
+ * (Egypt), is ignored.
+ */
+bool isRtlLanguage(String languageString) {
+  return const RegExp(@'^(ar|dv|he|iw|fa|nqo|ps|sd|ug|ur|yi|.*[-_]'
+      @'(Arab|Hebr|Thaa|Nkoo|Tfng))(?!.*[-_](Latn|Cyrl)($|-|_))'
+      @'($|-|_)', ignoreCase : true).hasMatch(languageString);
+}
+
+/**
+ * Enforce the [html] snippet in RTL directionality regardless of overall
+ * context. If the html piece was enclosed by a tag, the direction will be 
+ * applied to existing tag, otherwise a span tag will be added as wrapper.
+ * For this reason, if html snippet start with with tag, this tag must enclose
+ * the whole piece. If the tag already has a direction specified, this new one
+ * will override existing one in behavior (should work on Chrome, FF, and IE
+ * since this was ported directly from the Closure version).
+ */
+String enforceRtlInHtml(String html) {
+  return _enforceInHtmlHelper(html, 'rtl');
+}
+
+/**
+ * Enforce RTL on both end of the given [text] using unicode BiDi formatting
+ * characters RLE and PDF.
+ */
+String enforceRtlInText(String text) {
+  return '$RLE$text$PDF';
+}
+
+/**
+ * Enforce the [html] snippet in LTR directionality regardless of overall
+ * context. If the html piece was enclosed by a tag, the direction will be 
+ * applied to existing tag, otherwise a span tag will be added as wrapper.
+ * For this reason, if html snippet start with with tag, this tag must enclose
+ * the whole piece. If the tag already has a direction specified, this new one
+ * will override existing one in behavior (tested on FF and IE).
+ */
+String enforceLtrInHtml(String html) {
+  return _enforceInHtmlHelper(html, 'ltr');
+}
+
+/**
+ * Enforce LTR on both end of the given [text] using unicode BiDi formatting
+ * characters LRE and PDF.
+ */
+String enforceLtrInText(String text) {
+  return '$LRE$text$PDF';
+}
+
+/**
+ * Enforce the [html] snippet in the desired [direction] regardless of overall
+ * context. If the html piece was enclosed by a tag, the direction will be 
+ * applied to existing tag, otherwise a span tag will be added as wrapper.
+ * For this reason, if html snippet start with with tag, this tag must enclose
+ * the whole piece. If the tag already has a direction specified, this new one
+ * will override existing one in behavior (tested on FF and IE).
+ */
+String _enforceInHtmlHelper(String html, String direction) {
+  if (html.startsWith('<')) {
     StringBuffer buffer = new StringBuffer();
     var startIndex = 0;
-    Iterable matches = regexp.allMatches(str);
-    for (Match match in matches) {
-      buffer.add(str.substring(startIndex, match.start())).add(before);
-      buffer.add(str.substring(match.start(), match.end())).add(after);
+    Match match = const RegExp('<\\w+').firstMatch(html);
+    if (match != null) {
+      buffer.add(html.substring(
+          startIndex, match.end())).add(' dir=$direction');
       startIndex = match.end();
     }
-    return buffer.add(str.substring(startIndex)).toString();
-  }
-
-  /**
-   * Estimates the directionality of [text] using the best known
-   * general-purpose method (using relative word counts). A 
-   * TextDirection.UNKNOWN return value indicates completely neutral input.
-   * [isHtml] is true if [text] HTML or HTML-escaped.
-   *
-   * If the number of RTL words is above a certain percentage of the total
-   * number of strongly directional words, returns RTL.
-   * Otherwise, if any words are strongly or weakly LTR, returns LTR.
-   * Otherwise, returns UNKNOWN, which is used to mean `neutral`.
-   * Numbers and URLs are counted as weakly LTR.
-   */
-  static TextDirection estimateDirection(String text, [bool isHtml=false]) {
-    text = isHtml? stripHtmlIfNeeded(text) : text;
-    var rtlCount = 0;
-    var total = 0;
-    var hasWeaklyLtr = false;
-    // Split a string into 'words' for directionality estimation based on
-    // relative word counts.
-    for (String token in text.split(const RegExp(@'\s+'))) {
-      if (BidiUtils.startsWithRtl(token)) {
-        rtlCount++;
-        total++;
-      } else if (const RegExp(@'^http://').hasMatch(token)) {
-        // Checked if token looks like something that must always be LTR even in
-        // RTL text, such as a URL.
-        hasWeaklyLtr = true;
-      } else if (BidiUtils.hasAnyLtr(token)) {
-        total++;
-      } else if (const RegExp(@'\d').hasMatch(token)) {
-        // Checked if token contains any numerals.
-        hasWeaklyLtr = true;
-      }
+    return buffer.add(html.substring(startIndex)).toString();
+  }
+  // '\n' is important for FF so that it won't incorrectly merge span groups.
+  return '\n<span dir=$direction>$html</span>';
+}
+
+/**
+ * Apply bracket guard to [str] using html span tag. This is to address the 
+ * problem of messy bracket display that frequently happens in RTL layout.
+ * If [isRtlContext] is true, then we explicitly want to wrap in a span of RTL
+ * directionality, regardless of the estimated directionality.
+ */
+String guardBracketInHtml(String str, [bool isRtlContext]) {
+  var useRtl = isRtlContext == null ? hasAnyRtl(str) : isRtlContext;
+  RegExp matchingBrackets = 
+      const RegExp(@'(\(.*?\)+)|(\[.*?\]+)|(\{.*?\}+)|(&lt;.*?(&gt;)+)');
+  return _guardBracketHelper(str, matchingBrackets,
+      '<span dir=${useRtl? "rtl" : "ltr"}>', '</span>');
+}
+
+/**
+ * Apply bracket guard to [str] using LRM and RLM. This is to address the 
+ * problem of messy bracket display that frequently happens in RTL layout.
+ * This version works for both plain text and html, but in some cases is not
+ * as good as guardBracketInHtml.
+ * If [isRtlContext] is true, then we explicitly want to wrap in a span of RTL
+ * directionality, regardless of the estimated directionality.
+ */
+String guardBracketInText(String str, [bool isRtlContext]) {
+  var useRtl = isRtlContext == null ? hasAnyRtl(str) : isRtlContext;
+  var mark = useRtl ? RLM : LRM;
+  return _guardBracketHelper(str,
+      const RegExp(@'(\(.*?\)+)|(\[.*?\]+)|(\{.*?\}+)|(<.*?>+)'), mark, mark);
+}
+
+/**
+ * (Mostly) reimplements the $& functionality of "replace" in JavaScript.
+ * Given a [str] and the [regexp] to match with, optionally supply a string to
+ * be inserted [before] the match and/or [after]. For example, 
+ * `_guardBracketHelper('firetruck', const RegExp('truck'), 'hydrant', '!')`
+ * would return 'firehydrant!'.
+ */
+// TODO(efortuna): Get rid of this once this is implemented in Dart.
+// See Issue 2979.
+String _guardBracketHelper(String str, RegExp regexp, [String before,
+    String after]) {
+  StringBuffer buffer = new StringBuffer();
+  var startIndex = 0;
+  Iterable matches = regexp.allMatches(str);
+  for (Match match in matches) {
+    buffer.add(str.substring(startIndex, match.start())).add(before);
+    buffer.add(str.substring(match.start(), match.end())).add(after);
+    startIndex = match.end();
+  }
+  return buffer.add(str.substring(startIndex)).toString();
+}
+
+/**
+ * Estimates the directionality of [text] using the best known
+ * general-purpose method (using relative word counts). A 
+ * TextDirection.UNKNOWN return value indicates completely neutral input.
+ * [isHtml] is true if [text] HTML or HTML-escaped.
+ *
+ * If the number of RTL words is above a certain percentage of the total
+ * number of strongly directional words, returns RTL.
+ * Otherwise, if any words are strongly or weakly LTR, returns LTR.
+ * Otherwise, returns UNKNOWN, which is used to mean `neutral`.
+ * Numbers and URLs are counted as weakly LTR.
+ */
+TextDirection estimateDirectionOfText(String text, [bool isHtml=false]) {
+  text = isHtml? stripHtmlIfNeeded(text) : text;
+  var rtlCount = 0;
+  var total = 0;
+  var hasWeaklyLtr = false;
+  // Split a string into 'words' for directionality estimation based on
+  // relative word counts.
+  for (String token in text.split(const RegExp(@'\s+'))) {
+    if (startsWithRtl(token)) {
+      rtlCount++;
+      total++;
+    } else if (const RegExp(@'^http://').hasMatch(token)) {
+      // Checked if token looks like something that must always be LTR even in
+      // RTL text, such as a URL.
+      hasWeaklyLtr = true;
+    } else if (hasAnyLtr(token)) {
+      total++;
+    } else if (const RegExp(@'\d').hasMatch(token)) {
+      // Checked if token contains any numerals.
+      hasWeaklyLtr = true;
     }
-
-    if (total == 0) {
-      return hasWeaklyLtr ? TextDirection.LTR : TextDirection.UNKNOWN;
-    } else if (rtlCount > BidiUtils._RTL_DETECTION_THRESHOLD * total) {
-      return TextDirection.RTL;
+  }
+
+  if (total == 0) {
+    return hasWeaklyLtr ? TextDirection.LTR : TextDirection.UNKNOWN;
+  } else if (rtlCount > _RTL_DETECTION_THRESHOLD * total) {
+    return TextDirection.RTL;
+  } else {
+    return TextDirection.LTR;
+  }
+}
+
+/**
+ * Find the first index in [str] of the first closing parenthesis that does
+ * not match an opening parenthesis.
+ */
+int _unmatchedParenIndex(String str) {
+  int sum = 0;
+  int index = 0;
+  while (sum >= 0 || index > str.length) {
+    int char = str.charCodeAt(index);
+    if (char == '('.charCodeAt(0)) sum++;
+    else if (char == ')'.charCodeAt(0)) sum--;
+    index++;
+  }
+  return index;
+}
+
+/**
+ * Replace the double and single quote directly after a Hebrew character in
+ * [str] with GERESH and GERSHAYIM. This is most likely the user's intention.
+ */
+String normalizeHebrewQuote(String str) {
+  StringBuffer buf = new StringBuffer();
+  if (str.length > 0) {
+    buf.add(str.substring(0, 1));
+  }
+  // Start at 1 because we're looking for the patterns [\u0591-\u05f2])" or
+  // [\u0591-\u05f2]'.
+  for (int i = 1; i < str.length; i++) {
+    if (str.substring(i, i+1) == '"'
+        && const RegExp('[\u0591-\u05f2]').hasMatch(str.substring(i-1, i))) {
+      buf.add('\u05f4');
+    } else if (str.substring(i, i+1) == "'"
+        && const RegExp('[\u0591-\u05f2]').hasMatch(str.substring(i-1, i))) {
+      buf.add('\u05f3');
     } else {
-      return TextDirection.LTR;
+      buf.add(str.substring(i, i+1));
     }
   }
-
-  /**
-   * Find the first index in [str] of the first closing parenthesis that does
-   * not match an opening parenthesis.
-   */
-  static int _unmatchedParenIndex(String str) {
-    int sum = 0;
-    int index = 0;
-    while (sum >= 0 || index > str.length) {
-      int char = str.charCodeAt(index);
-      if (char == '('.charCodeAt(0)) sum++;
-      else if (char == ')'.charCodeAt(0)) sum--;
-      index++;
-    }
-    return index;
-  }
-
-  /**
-   * Replace the double and single quote directly after a Hebrew character in
-   * [str] with GERESH and GERSHAYIM. This is most likely the user's intention.
-   */
-  static String normalizeHebrewQuote(String str) {
-    StringBuffer buf = new StringBuffer();
-    if (str.length > 0) {
-      buf.add(str.substring(0, 1));
-    }
-    // Start at 1 because we're looking for the patterns [\u0591-\u05f2])" or
-    // [\u0591-\u05f2]'.
-    for (int i = 1; i < str.length; i++) {
-      if (str.substring(i, i+1) == '"'
-          && const RegExp('[\u0591-\u05f2]').hasMatch(str.substring(i-1, i))) {
-        buf.add('\u05f4');
-      } else if (str.substring(i, i+1) == "'"
-          && const RegExp('[\u0591-\u05f2]').hasMatch(str.substring(i-1, i))) {
-        buf.add('\u05f3');
-      } else {
-        buf.add(str.substring(i, i+1));
-      }
-    }
-    return buf.toString();
-  }
-
-  /**
-   * Check the directionality of [str], return true if the piece of
-   * text should be laid out in RTL direction. If [isHtml] is true, the string
-   * is HTML or HTML-escaped.
-   */
-  static bool detectRtlDirectionality(String str, [bool isHtml]) {
-    return estimateDirection(str, isHtml) == TextDirection.RTL;
-  }
-}
+  return buf.toString();
+}
+
+/**
+ * Check the estimated directionality of [str], return true if the piece of
+ * text should be laid out in RTL direction. If [isHtml] is true, the string
+ * is HTML or HTML-escaped.
+ */
+bool detectRtlDirectionality(String str, [bool isHtml]) {
+  return estimateDirectionOfText(str, isHtml) == TextDirection.RTL;
+}