Basic REs

• '|', '+', and '?' are ordinary characters and there is no equivalent for their functionality
• The delimiters for bounds are '\{' and '\}', with '{' and '}' by themselves ordinary characters
• The parentheses for nested subexpressions are '\(' and '\)', with '(' and ')' by themselves ordinary characters
• '^' is an ordinary character except at the beginning of the RE or(!) the beginning of a parenthesized subexpression
• '$' is an ordinary character except at the end of the RE or(!) the end of a parenthesized subexpression
• '*' is an ordinary character if it appears at the beginning of the RE or the beginning of a parenthesized subexpression (after a possible leading '^')
• There is one new type of atom, a back reference: '\' followed by a nonzero decimal digit d matches the same sequence of characters matched by the dth parenthesized subexpression (numbering subexpressions by the positions of their opening parentheses, left to right), so that (e.g.) '\([bc]\)\1' matches 'bb' or 'cc' but not 'bc'