Request: ?json_string, similar to ?js_string

Hi,

FreeMarker today comes with the built-in "?js_string", which escapes
strings according to JavaScript rules. From the FreeMarker docs:

Escapes the string with the escaping rules of JavaScript language string
> literals, so it is safe to insert the value into a string literal. Both
> quotation mark (") and apostrophe-quoate (') are escaped. Starting from
> FreeMarker 2.3.1, it also escapes > as \> (to avoid </script>).
> Furthermore, all characters under UCS<http://freemarker.org/docs/gloss.html#gloss.UCS> code
> point 0x20, that has no dedicated escape sequence in JavaScript language,
> will be replaced with hexadecimal escape (\x*XX*). (Of course, according
> the JavaScript language string literal syntax, backslash (\) will be
> escaped too, line-feed will be escaped as \n, ...etc.)


However, this is not valid json. In particular, the native JSON javascript
object in newer browsers do not support all those escape characters. An
example of problems can be found on stackoverflow:
http://stackoverflow.com/questions/2275359/jquery-single-quote-in-json-response


In case a single-quote pops up, ?js_script will escape it which again leads
> to invalid JSON. The hotfix for it is: ${variable?js_string?replace("\'",
> "\'")} and if you really want to be picky:
> ${variable?js_string?replace("\'", "\'")?replace("\>",">")}


The formal grammar for legal json escapes are shown in the spec, at
http://es5.github.com/#x15.12.1. The excerpt below shows legal escape
characters (in additon, any character can be escaped using its numeric
unicode sequence):

JSONEscapeCharacter :: one of
> " / \ b f n r t


The questions, then, would be something like this:

a) Should FreeMarker support ?json_string, similar to js_string?
b) Is there interest in a patch, or is it better that those who know the
code inside-out create it in the first place?

-- 
Eirik

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