Regular exp[ression in XSLT

Question

Can somebody help me to understand this below regular expreesion in XSLT.

regexp:match(test-graph.api.example.com, '(?=CN).*\.(.*)(\.)(.*)(?<=com)', 'i')

What would be the output and how to interpret this regular expression.

Please let me know

Answer 1

Is should be read this way:

(?=CN).*\.(.*)(\.)(.*)(?<=com)

explanation:

.* matches any character (except for line terminators)
    * Quantifier — Matches between zero and unlimited times, as many times as possible, giving back as needed (greedy)
\. matches the character . literally (case sensitive)
1st Capturing Group (.*)
.* matches any character (except for line terminators)
    * Quantifier — Matches between zero and unlimited times, as many times as possible, giving back as needed (greedy)
2nd Capturing Group (\.)
\. matches the character . literally
3rd Capturing Group (.*)
.* matches any character (except for line terminators)
    * Quantifier — Matches between zero and unlimited times, as many times as possible, giving back as needed (greedy)
Positive Lookbehind (?<=com)
Assert that the Regex below matches
com matches the characters com literally 

The i modifiers means that the regex is case insentive.