Regex in setvar variables

Context:
Currently, (unescaped) backslashes are forbidden in variables content.
In msre_parse_generic():

if (*p == '\\') {
   if ((*(p + 1) == '\0') || ((*(p + 1) != '\'') && (*(p + 1) != '\\'))) {
      [error & return]
   }
   p++;

The only case a backslash is accepted is when it escapes a single quote or a backslash.

Problem:
You cannot store a regex in a variable: setvar:'tx.var=\babc\b'
When doing this manually, you can escape the string obviously: setvar:'tx.var=\babc\b'
But when you use a macro like the following:

<Macro MyMacro $regex>
 SecAction ...,setver:'var=$regex',...
 SecRule ARG "$regex" ...
</Macro>

there's no way to call the macro with a parameter compatible with both directives

Solution:
We could be lax (and still compatible with the current behaviour):

• If it's followed by a quote or a backslash, accept and "eats" the escaping backslash
• In all other cases, accept and don't "eat" the backslash
• the code change is trivial

Does somebody see any other solution?

Start in msre_parse_generic(), where backslashes in variable content are currently rejected unless they escape a quote or another backslash. Exercise setvar values containing regexes and macro parameters, then verify that quote and backslash escapes are consumed while other backslashes are preserved.