function escape(ch) {
      return '\\\\\\' + ch;
    }
@ngdoc method
@name $interpolateProvider#endSymbol
@description
Symbol to denote the end of expression in the interpolated string. Defaults to `}}`.

@param {string=} value new value to set the ending symbol to.
@returns {string|self} Returns the symbol when used as getter and self if used as setter.