ASF Bug 57136 – EL Parser escaping dollar sign not ${ or ${...}
Ensure only \${ and #{ are treated as escapes for ${ and #{ rather than \$ and # being treated as escapes for $ and # when processing literal expressions in expression language.

In the EL 3.0 spec it says...
Alternatively, the escape characters \$ and # can be used to escape what would
otherwise be treated as an eval-expression. Given the literal-expressions:
\${exprA}
#

.

That means it should not escape lets say "Price:
$500.00" it should instead output "Price: \$500.00"(it currently would output "Price: $500.00") but should instead escape "Price:
${500.00}" and the output of that would be "Price: ${500.00}".

Normally this wouldn't be run into, but I happened to run into this issue passing javascript code through the EL processor, that happens to have some escaped dollar signs inside some regex strings.

It maybe a little more acceptable to use \${ and #{ as the escapes, as that is a better indication that there is about to be an expression

https://bz.apache.org/bugzilla/show_bug.cgi?id=57136
http://svn.apache.org/r1658351
http://svn.apache.org/r1658940