newpat = optionalPattern(pat)
creates a pattern that matches pat when possible, but matching
pat is not required for a pattern expression to match successfully. Use
this function in conjunction with other pattern functions to build patterns that are more
flexible in their matching requirements.
Use optionalPattern to designate a pattern as optional to match.
Create txt as a string. Create a pattern, pat, that matches "foo" and will optionally match "bar" so long as it is preceded by "foo". Extract the pattern.
txt = "foo bar foobar";
pat = "foo" + optionalPattern("bar");
extract(txt,pat)
Build a pattern that matches combinations of letters and periods after an "@". Use optionPattern to match subdomains if present. If a subdomain is not present, optionalPattern does not prevent a match if other conditions of pat are met. Extract the pattern.
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