Digit separators for numeric literals

Hi internals! A while ago a question was asked on the php-general mailing list with regard to digit seperators in numeric literals[1]. IMHO it might be a useful enhancement to allow such digit separators for numeric (integer and float) literals in PHP for better readability; several other languages already support them (such as Java, Perl, Ruby, C#, Eiffel and C++14). Before attempting to draft a respective RFC, I'd like to get some feedback, whether this is generally considered to be useful, which character would be preferred (most other languages seem to allow the underscore, but an apostroph or maybe some other character might be reasonable as well), and which restrictions should be applied (e.g. arbitrary use of the separator, group thousands only, etc.) I'm looking forward to hear your opinion. Thanks in advance. [1] <http://marc.info/?l=php-general&m=142143581810951&w=2> -- Christoph M. Becker