Description:
------------
output_add_rewrite_var() fails to operate on forms with attributes containing underscores:
<form _url="..">...</form>

The reason is that only a-zA-Z are allowed in attribute names:
ext/standard/url_scanner_ex.re, lines 310-...:
state_arg:
	start = YYCURSOR;
/*!re2c
  alpha alphadash*	{ passthru(STD_ARGS); handle_arg(STD_ARGS); STATE = STATE_BEFORE_VAL; goto state_before_val; }
  any		{ passthru(STD_ARGS); STATE = STATE_NEXT_ARG; goto state_next_arg; }
*/

and alpha is:
alpha = [a-zA-Z];


I know that _ is not a character that is used in any standard html attributes, but it's used sometimes in the dojo world.