# Matches most PHP tags
\<                       # An open Caret
\?                       # Follow by a Question Mark
(?>                      # Followed by one of the following: 
    (?<IsFullTag>php)|   # The literal text "php" OR 
    (?<IsEchoTag>=)      # An equal sign (denoting an echo tag)
)?                       # If neither was present, it's a ShortTag
\s{1,}                   # At least one whitespace character
(?<Content>(?:.|\s)+?)     # Any characters until
(?=\?\>)                 # the closing tag. 
\?\>                     # Then the closing tag.