title: Universal Subset of Regex Grammars? Or comprehensive table of features per grammar
body: <p>Is there a subset of regex features that are considered to be the same/available within all major grammars?  For example, <code>.</code> seems to be available and has the same meaning everywhere.  I suspect <code>*</code>, <code>+</code>, <code>^</code>, <code>$</code> are like this as well.</p>
  
  <p>A broader search tends to show comparisons of a few features of a few grammars with notes/caveats that this grammar is like that one, or derived from that one, etc. I know I can do the work, but I am asking if there is an existing reference to a subset like this.</p>
  
  <p>To narrow this question down further (maybe), is there a subset such that expressions using that set would work the same in C++11 no matter which grammar-specifying parameter was passed to <code>std::regex()</code>?</p>
  
  <p><strong>Note to those who have voted to close this as a duplicate:</strong>
  The question you claim is a duplicate has no qualifiers next to several features that are not universal even in the subset of grammars that are supported by C++11.  For example - *?:reluctant, *+:possessive, ():capture groups, Lookaheads: (?=...) and perhaps others.  Some of these resulted in an EXCEPTION being thrown just by adding them to a std::regex() pattern.</p>