C# - Alternation Constructs Regular Expressions

Alternation constructs modify a regular expression to enable either/or matching. The following table lists the alternation constructs −

Alternation construct Description Pattern Matches
| Matches any one element separated by the vertical bar (|) character. th(e|is|at) "the", "this" in "this is the day. "
(?( expression )yes | no ) Matches yes if expression matches; otherwise, matches the optional no part. Expression is interpreted as a zero-width assertion. (?(A)A\d{2}\b|\b\d{3}\b) "A10", "910" in "A10 C103 910"
(?( name )yes | no ) Matches yes if the named capture name has a match; otherwise, matches the optional no. (?< quoted>")?(?(quoted).+?"|\S+\s) Dogs.jpg, "Yiska playing.jpg" in "Dogs.jpg "Yiska playing.jpg""