BOL BOL, no Match "" at beginning of line.
MBOL BOL, no Same, assuming multiline.
SBOL BOL, no Same, assuming singleline.
+EOS EOL, no Match "" at end of string.
EOL EOL, no Match "" at end of line.
MEOL EOL, no Same, assuming multiline.
SEOL EOL, no Same, assuming singleline.
GPOS GPOS, no Matches where last m//g left off.
# [Special] alternatives
-ANY ANY, no Match any one character (except newline).
-SANY ANY, no Match any one character.
+REG_ANY REG_ANY, no Match any one character (except newline).
+SANY REG_ANY, no Match any one character.
+CANY REG_ANY, no Match any one byte.
ANYOF ANYOF, sv Match character in (or not in) this class.
ALNUM ALNUM, no Match any alphanumeric character
ALNUML ALNUM, no Match any alphanumeric char in locale
NSPACE NSPACE, no Match any non-whitespace character
NSPACEL NSPACE, no Match any non-whitespace char in locale
DIGIT DIGIT, no Match any numeric character
+DIGITL DIGIT, no Match any numeric character in locale
NDIGIT NDIGIT, no Match any non-numeric character
+NDIGITL NDIGIT, no Match any non-numeric character in locale
+CLUMP CLUMP, no Match any combining character sequence
# BRANCH The set of branches constituting a single choice are hooked
# together with their "next" pointers, since precedence prevents
EXACTF EXACT, sv Match this string, folded (prec. by length).
EXACTFL EXACT, sv Match this string, folded in locale (w/len).
+# Trie Related (behave the same as A|LIST|OF|WORDS would)
+TRIE TRIE, trie 1 Match one or more of many EXACT strings
+TRIEF TRIE, trie 1 Match one or more of many EXACTF strings
+TRIEFL TRIE, trie 1 Match one or more of many EXACTFL strings
+
# Do nothing
NOTHING NOTHING,no Match empty string.
# A variant of above which delimits a group, thus stops optimizations