Function XRegExp

docs/tests/v2/es6/js/sanddance.js:139471–139550

* Creates an extended regular expression object for matching text with a pattern. Differs from a * native regular expression in that additional syntax and flags are supported. The returned object * is in fact a native `RegExp` and works with all native methods. * * @class XRegExp * @constructor

(pattern, flags)

 * XRegExp(/regex/);
 */
function XRegExp(pattern, flags) {
    if (XRegExp.isRegExp(pattern)) {
        if (flags !== undefined) {
            throw new TypeError('Cannot supply flags when copying a RegExp');
        }
        return copyRegex(pattern);
    }

    // Copy the argument behavior of `RegExp`
    pattern = pattern === undefined ? '' : String(pattern);
    flags = flags === undefined ? '' : String(flags);

    if (XRegExp.isInstalled('astral') && !(flags.indexOf('A') !== -1)) {
        // This causes an error to be thrown if the Unicode Base addon is not available
        flags += 'A';
    }

    if (!patternCache[pattern]) {
        patternCache[pattern] = {};
    }

    if (!patternCache[pattern][flags]) {
        var context = {
            hasNamedCapture: false,
            captureNames: []
        };
        var scope = defaultScope;
        var output = '';
        var pos = 0;
        var result = void 0;

        // Check for flag-related errors, and strip/apply flags in a leading mode modifier
        var applied = prepareFlags(pattern, flags);
        var appliedPattern = applied.pattern;
        var appliedFlags = applied.flags;

        // Use XRegExp's tokens to translate the pattern to a native regex pattern.
        // `appliedPattern.length` may change on each iteration if tokens use `reparse`
        while (pos < appliedPattern.length) {
            do {
                // Check for custom tokens at the current position
                result = runTokens(appliedPattern, appliedFlags, pos, scope, context);
                // If the matched token used the `reparse` option, splice its output into the
                // pattern before running tokens again at the same position
                if (result && result.reparse) {
                    appliedPattern = appliedPattern.slice(0, pos) + result.output + appliedPattern.slice(pos + result.matchLength);
                }
            } while (result && result.reparse);

            if (result) {
                output += result.output;
                pos += result.matchLength || 1;
            } else {
                // Get the native token at the current position
                var token = XRegExp.exec(appliedPattern, nativeTokens[scope], pos, 'sticky')[0];
                output += token;
                pos += token.length;
                if (token === '[' && scope === defaultScope) {