diff options
Diffstat (limited to 'txr.1')
| -rw-r--r-- | txr.1 | 9 |
1 files changed, 5 insertions, 4 deletions
@@ -644,10 +644,11 @@ consisting of the empty string; i.e. it matches no characters. The empty string can appear alone as a full regular expression (for instance the .B txr syntax @// with nothing between the slashes) -and can also be used as a subexpression term for some operators. The -expression a| means (a|): match either a, or nothing. It's not possible to -pass the empty regex to some operators; for instance (*) is a syntax error, -not the * operator with an empty string on the left. +and can also be passed as a subexpression to operators, though this +may require the use of parentheses to make the empty regex explicit. For +example, the expression a| means: match either a, or nothing. The forms +* and (*) are syntax errors; the correct way to match the empty expression +zero or more times is the syntax ()*. .IP (R) If R is a regular expression, then so is (R). The contents of parentheses denote one regular expression unit, so that for |