Have you took a look at the link I provided above: http://www.regular-expressions.info/tutorial.html
Thanks for the reference, I also looked at
http://en.wikipedia.org/wiki/Regex for a more concise but cryptic explanation.
Decided my two main series search patterns should be
(?i)^.*\\(?P<title>[^\\]*?)\bs(?P<season>[0-9]{1,2})[ .x]{0,2}e(?P<episode>[0-9]{1,2})\b[ .-]*(?P<epititle>[^\\]*)$
(?i)^.*\\(?P<title>[^\\]*?)[ .-]*\b(?P<season>[0-9]{1,2})x(?P<episode>[0-9]{1,2})\b[ .-]*(?P<epititle>[^\\]*)$
They basically look for a file name containing text of the form "s11e11" or "11x11" bounded by word boundaries. Where the s11 & e11 can be separated by " ", "-" or "x"
I usually store my TV series in the format
Title\s1\episode file
So I precede the above by directory structure searches i.e. Look for “Title\s1\” and use this data in preference. File names are searched from more to less stringent formats i.e. Look for “Title\s1\” with file name formats
text s0e00 episode title
text 00x00 episode title
Text 0 optional not digit 00 episode title (digit but not word boundary required)
text 00 episode title
My regex for which are
(?i)^.*\\(?P<title>[^\\]*)\\s(?P<season>[0-9]{1,2})\\[^\\]*?\bs([0-9]{1,2})[ .x]{0,2}e(?P<episode>[0-9]{1,2})\b[ .-]*(?P<epititle>[^\\]*)$
(?i)^.*\\(?P<title>[^\\]*)\\s(?P<season>[0-9]{1,2})\\[^\\]*?\b[0-9]{1,2}x(?P<episode>[0-9]{1,2})\b[ .-]*(?P<epititle>[^\\]*)$
(?i)^.*\\(?P<title>[^\\]*)\\s(?P<season>[0-9]{1,2})\\[^\\]*?(?<![0-9])[0-9]{1,2}[^\\0-9]*(?P<episode>[0-9]{2})(?![0-9])[ .-]*(?P<epititle>[^\\]*)$
(?i)^.*\\(?P<title>[^\\]*)\\s(?P<season>[0-9]{1,2})\\[^\\]*?(?<![s0-9])(?P<episode>[0-9]{2})(?![0-9])[ .-]*(?P<epititle>[^\\]*)$
Hope this helps some others despite the fact it is not yet working 100% as expected
Edit
regex updated