find: emacs regular expression syntax

1 
1 8.5.4 'emacs' regular expression syntax
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1 
1 The character '.' matches any single character except newline.
1 
1 '+'
1      indicates that the regular expression should match one or more
1      occurrences of the previous atom or regexp.
1 '?'
1      indicates that the regular expression should match zero or one
1      occurrence of the previous atom or regexp.
1 '\+'
1      matches a '+'
1 '\?'
1      matches a '?'.
1 
1    Bracket expressions are used to match ranges of characters.  Bracket
1 expressions where the range is backward, for example '[z-a]', are
1 ignored.  Within square brackets, '\' is taken literally.  Character
1 classes are not supported, so for example you would need to use '[0-9]'
1 instead of '[[:digit:]]'.
1 
1    GNU extensions are supported:
1 
1   1. '\w' matches a character within a word
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1   2. '\W' matches a character which is not within a word
1 
1   3. '\<' matches the beginning of a word
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1   4. '\>' matches the end of a word
1 
1   5. '\b' matches a word boundary
1 
1   6. '\B' matches characters which are not a word boundary
1 
1   7. '\`' matches the beginning of the whole input
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1   8. '\'' matches the end of the whole input
1 
1    Grouping is performed with backslashes followed by parentheses '\(',
1 '\)'.  A backslash followed by a digit acts as a back-reference and
1 matches the same thing as the previous grouped expression indicated by
1 that number.  For example '\2' matches the second group expression.  The
1 order of group expressions is determined by the position of their
1 opening parenthesis '\('.
1 
1    The alternation operator is '\|'.
1 
1    The character '^' only represents the beginning of a string when it
1 appears:
1 
1   1. At the beginning of a regular expression
1 
1   2. After an open-group, signified by '\('
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1   3. After the alternation operator '\|'
1 
1    The character '$' only represents the end of a string when it
1 appears:
1 
1   1. At the end of a regular expression
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1   2. Before a close-group, signified by '\)'
1   3. Before the alternation operator '\|'
1 
1    '*', '+' and '?' are special at any point in a regular expression
1 except:
1 
1   1. At the beginning of a regular expression
1 
1   2. After an open-group, signified by '\('
1   3. After the alternation operator '\|'
1 
1    The longest possible match is returned; this applies to the regular
1 expression as a whole and (subject to this constraint) to subexpressions
1 within groups.
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