to
Converts the input value to a string. If the input is null, the result is "". If the input is a #types-boolean, the result is "true" or "false". If the input is a number, it is converted to a string as specified by the "NumberToString" algorithm of the ECMAScript Language Specification. If the input is a #color, it is converted to a string of the form "rgba(r,g,b,a)", where r, g, and b are numerals ranging from 0 to 255, and a ranges from 0 to 1. If the input is an #types-image expression, 'to-string' returns the image name. Otherwise, the input is converted to a string in the format specified by the JSON.stringify function of the ECMAScript Language Specification.