Regular Expressions 101

^start of string

Group WFF(?P<WFF>(?P<L>~*(?>[A-Z\^!]|$\g<WFF>$))(?(?=\$)\$\g<L>|(?:(?P<O>[\%&|])(?:\g<L>\k<O>)*\g<L>)?))

Group L(?P<L>~*(?>[A-Z\^!]|$\g<WFF>$))

~*the literal ~ (126₁₀ / 176₈ / 7E₁₆) , repeated any number of times

Atomic Group(?>[A-Z\^!]|$\g<WFF>$)

1st Alternative[A-Z\^!]

Character Class[A-Z\^!]

A-Zone character from A (65₁₀) to Z (90₁₀) (case sensitive)

\^the literal ^ (94₁₀ / 136₈ / 5E₁₆)

!the literal ! (33₁₀ / 41₈ / 21₁₆)

2nd Alternative$\g<WFF>$

\(the literal ( (40₁₀ / 50₈ / 28₁₆)

\g<WFF>calls group WFF as a subroutine

\)the literal ) (41₁₀ / 51₈ / 29₁₆)

Condition(?(?=\$)\$\g<L>|(?:(?P<O>[\%&|])(?:\g<L>\k<O>)*\g<L>)?)

Uses the first branch if the lookaround matches

Positive Lookahead(?=\$)

\$the literal $ (36₁₀ / 44₈ / 24₁₆)

If the condition is true, match this branch:\$\g<L>

\$the literal $ (36₁₀ / 44₈ / 24₁₆)

\g<L>calls group L as a subroutine

Otherwise, match this branch:(?:(?P<O>[\%&|])(?:\g<L>\k<O>)*\g<L>)?

Non-Capturing Group(?:(?P<O>[\%&|])(?:\g<L>\k<O>)*\g<L>)?

?repeats the group contents below at most once:

Group O(?P<O>[\%&|])

Character Class[\%&|]

\%the literal % (37₁₀ / 45₈ / 25₁₆)

&the literal & (38₁₀ / 46₈ / 26₁₆)

|the literal | (124₁₀ / 174₈ / 7C₁₆)

Non-Capturing Group(?:\g<L>\k<O>)*

*repeats the group contents below any number of times:

\g<L>calls group L as a subroutine

\k<O>the text saved by group O

\g<L>calls group L as a subroutine

$end of string, or before its final line terminator

Global pattern flags

g modifier: global. Finds all matches instead of stopping after the first

x modifier: extended. Ignores unescaped whitespace and comments outside character classes

Detailed match information will be displayed here automatically.

Search reference

Regular Expression

^(?P<WFF>(?P<L>~*(?>[A-Z\^!]|\(\g<WFF>\)))(?(?=\$)\$\g<L>|(?:(?P<O>[\%&|])(?:\g<L>\k<O>)*\g<L>)?))$

P&(Q$(R|S))