code: function _expandLanguageMap(languageMap) {
    var rval = [];
    var keys = Object.keys(languageMap).sort();
    for(var ki = 0; ki < keys.length; ++ki) {
      var key = keys[ki];
      var val = languageMap[key];
      if(!_isArray(val)) {
        val = [val];
      }
      for(var vi = 0; vi < val.length; ++vi) {
        var item = val[vi];
        if(!_isString(item)) {
          throw new JsonLdError(
            'Invalid JSON-LD syntax; language map values must be strings.',
            'jsonld.SyntaxError', {languageMap: languageMap});
        }
        rval.push({
          '@value': item,
          '@language': key.toLowerCase()
        });
      }
    }
    return rval;
  }
docs: Expands a language map.
  
  @param languageMap the language map to expand.
  
  @return the expanded language map.