Here's a quick list of all Proxomitron's special characters. See Matching Rules for more detailed explanations.

Matching meta characters

*	match a string of any characters.
?	match any single character.
[abc]	match any single character listed in the brackets.
[^a-z]	match any single character not listed in the brackets.
[#x:y]	numeric range match. Supports negative numbers.
" "	(a Space) Always matches but also consumes any whitespace.
\s	match string of whitespace only.
\w	match any number of non-space characters except ">".
\t	matches a single tab character.
\r	matches a single carriage return character.
\n	matches a single newline character.
\0-9	put match into a variable - works like "*" unless following stuff in parentheses: "( ... )\1"
\#	append match on to replacement stack.
&	AND function.
&&	AND-AND (like AND but limits scope of second part).
|	OR function.
(^...)	NOT function.
(...)	group a sub-expression. Negate with "(^ ... )"
+	repeat previous match until there are no more left.
++	same as '+' except matches to up to the point where what follows is true.
+{5}	the + or ++ pattern run will match only 5 repetitions.
+{2,7}	the + or ++ pattern run will match 2 to 7 repetitions.
+{3,*}	the + or ++ pattern run will match 3 or more repetitions.
\	escape any meta character's special meaning.
=	magic equal - absorbs leading/trailing spaces.
"	magic quote - matches double or single quote.
'	smart ending quote - use to deal with nested quotes.
<start>	insert this at the beginning of a page
<end>	insert this at the end of a page

Special Matching Commands

(m=matching value r=replacement text b=boolean value)

$AV(m)	match an attribute's value excluding any quotes
$AVQ(m)	match an attribute's value including any quotes
$CON(x,y,[z])	test current connection number
$ESC(stuff)	Escape special characters in a string to make it URL safe (reverse of $UESC)
$FILTER(b)	force filtering or not
$IHDR(header: m)	match input headers
$INEST(start,[m],end)	like nest, but assumes inital tag already matched
$JUMP(url)	redirect URL (non-transparent)
$LST(listname)	include a blocklist in any matching expression
$NEST(start,[m],end)	find pair of nested tags
$OHDR(header: m)	match output headers
$RDIR(url)	redirect URL (transparent)
$SET(0=r)	set a positional variable (\0-9 or \#) to a specific value.
$SETPROXY	select a particular proxy for connection .
$STOP()	turn filter off for rest of page
$TYPE(type value)	check type of page being processed
$UESC(stuff)	remove hexidecimal "%xx" style URL escapes
$URL(m)	match a the URL inside the matching portion of a filter.
$USEPROXY(b)	turn external proxy on or off for connection

Replacement Text Escapes

\0-9	Insert a variable into the replacement text.
\#	Inserts one item from the replacement stack each time it is used - first in first out
\@	Insert all the items in the replacement stack.
\\	Insert a single backslash.
\a	Insert any anchor text from a URL (anything following a "#").
\d	Insert The Proxomitron base directory in "file://" URL format.
\h	Insert the host portion of the URL.
\k	Kills the current connection.
\p	Insert the path portion of the URL.
\q	Insert any query string from a URL (anything following a "?").
\u	Insert the full URL of the current web page.