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Parentheses can be used as "memory" for relating different parts of a match or for relating substitution to match
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If a part of a regular expression is enclosed in parentheses, the MATCHED value is stored in temporary variables \1 \2 .. for first,second .. set of parentheses
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/Geoffrey(.*)Fox/ when matched to Geoffrey Charles Fox stores
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\1 = ' Charles ' which can be transferred to substitution string which could be
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/Geoffrey \(\1\) Fox/ for result Geoffrey ( Charles ) Fox
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Note ONLY use \1 \2 etc. in pattern. Use $1 $2 outside pattern
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Parentheses can also be used to clarify meaning of a regular expression by defining precedence of a set of operations and so distinguish for instance
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/(a|b)*/ from /a|(b*)/
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There is a definite convention for precendence but as usual I recommend using parantheses and in Perl5(later) we will see how to distinguish use of parantheses for either clarificatiuon or defining matched groups.
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