Initial revision
diff --git a/Lib/regex_syntax.py b/Lib/regex_syntax.py
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+++ b/Lib/regex_syntax.py
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+# These bits are passed to regex.set_syntax() to choose among
+# alternative regexp syntaxes.
+
+# 1 means plain parentheses serve as grouping, and backslash
+# parentheses are needed for literal searching.
+# 0 means backslash-parentheses are grouping, and plain parentheses
+# are for literal searching.
+RE_NO_BK_PARENS = 1
+
+# 1 means plain | serves as the "or"-operator, and \| is a literal.
+# 0 means \| serves as the "or"-operator, and | is a literal.
+RE_NO_BK_VBAR = 2
+
+# 0 means plain + or ? serves as an operator, and \+, \? are literals.
+# 1 means \+, \? are operators and plain +, ? are literals.
+RE_BK_PLUS_QM = 4
+
+# 1 means | binds tighter than ^ or $.
+# 0 means the contrary.
+RE_TIGHT_VBAR = 8
+
+# 1 means treat \n as an _OR operator
+# 0 means treat it as a normal character
+RE_NEWLINE_OR = 16
+
+# 0 means that a special characters (such as *, ^, and $) always have
+# their special meaning regardless of the surrounding context.
+# 1 means that special characters may act as normal characters in some
+# contexts. Specifically, this applies to:
+# ^ - only special at the beginning, or after ( or |
+# $ - only special at the end, or before ) or |
+# *, +, ? - only special when not after the beginning, (, or |
+RE_CONTEXT_INDEP_OPS = 32
+
+# Now define combinations of bits for the standard possibilities.
+RE_SYNTAX_AWK = (RE_NO_BK_PARENS | RE_NO_BK_VBAR | RE_CONTEXT_INDEP_OPS)
+RE_SYNTAX_EGREP = (RE_SYNTAX_AWK | RE_NEWLINE_OR)
+RE_SYNTAX_GREP = (RE_BK_PLUS_QM | RE_NEWLINE_OR)
+RE_SYNTAX_EMACS = 0
+
+# (Python's obsolete "regexp" module used a syntax similar to awk.)