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# Line 4  PCRE - Perl-compatible regular expressio Line 4  PCRE - Perl-compatible regular expressio
4  .SH "PCRE REGULAR EXPRESSION DETAILS"  .SH "PCRE REGULAR EXPRESSION DETAILS"
5  .rs  .rs
6  .sp  .sp
7  The syntax and semantics of the regular expressions supported by PCRE are  The syntax and semantics of the regular expressions that are supported by PCRE
8  described below. Regular expressions are also described in the Perl  are described in detail below. There is a quick-reference syntax summary in the
9  documentation and in a number of books, some of which have copious examples.  .\" HREF
10  Jeffrey Friedl's "Mastering Regular Expressions", published by O'Reilly, covers  \fBpcresyntax\fP
11  regular expressions in great detail. This description of PCRE's regular  .\"
12  expressions is intended as reference material.  page. PCRE tries to match Perl syntax and semantics as closely as it can. PCRE
13    also supports some alternative regular expression syntax (which does not
14    conflict with the Perl syntax) in order to provide some compatibility with
15    regular expressions in Python, .NET, and Oniguruma.
16    .P
17    Perl's regular expressions are described in its own documentation, and
18    regular expressions in general are covered in a number of books, some of which
19    have copious examples. Jeffrey Friedl's "Mastering Regular Expressions",
20    published by O'Reilly, covers regular expressions in great detail. This
21    description of PCRE's regular expressions is intended as reference material.
22  .P  .P
23  The original operation of PCRE was on strings of one-byte characters. However,  The original operation of PCRE was on strings of one-byte characters. However,
24  there is now also support for UTF-8 character strings. To use this, you must  there is now also support for UTF-8 character strings. To use this, you must
# Line 40  discussed in the Line 49  discussed in the
49  page.  page.
50  .  .
51  .  .
52    .SH "NEWLINE CONVENTIONS"
53    .rs
54    .sp
55    PCRE supports five different conventions for indicating line breaks in
56    strings: a single CR (carriage return) character, a single LF (linefeed)
57    character, the two-character sequence CRLF, any of the three preceding, or any
58    Unicode newline sequence. The
59    .\" HREF
60    \fBpcreapi\fP
61    .\"
62    page has
63    .\" HTML <a href="pcreapi.html#newlines">
64    .\" </a>
65    further discussion
66    .\"
67    about newlines, and shows how to set the newline convention in the
68    \fIoptions\fP arguments for the compiling and matching functions.
69    .P
70    It is also possible to specify a newline convention by starting a pattern
71    string with one of the following five sequences:
72    .sp
73      (*CR)        carriage return
74      (*LF)        linefeed
75      (*CRLF)      carriage return, followed by linefeed
76      (*ANYCRLF)   any of the three above
77      (*ANY)       all Unicode newline sequences
78    .sp
79    These override the default and the options given to \fBpcre_compile()\fP. For
80    example, on a Unix system where LF is the default newline sequence, the pattern
81    .sp
82      (*CR)a.b
83    .sp
84    changes the convention to CR. That pattern matches "a\enb" because LF is no
85    longer a newline. Note that these special settings, which are not
86    Perl-compatible, are recognized only at the very start of a pattern, and that
87    they must be in upper case. If more than one of them is present, the last one
88    is used.
89    .P
90    The newline convention does not affect what the \eR escape sequence matches. By
91    default, this is any Unicode newline sequence, for Perl compatibility. However,
92    this can be changed; see the description of \eR in the section entitled
93    .\" HTML <a href="#newlineseq">
94    .\" </a>
95    "Newline sequences"
96    .\"
97    below. A change of \eR setting can be combined with a change of newline
98    convention.
99    .
100    .
101  .SH "CHARACTERS AND METACHARACTERS"  .SH "CHARACTERS AND METACHARACTERS"
102  .rs  .rs
103  .sp  .sp
# Line 149  represents: Line 207  represents:
207    \ecx       "control-x", where x is any character    \ecx       "control-x", where x is any character
208    \ee        escape (hex 1B)    \ee        escape (hex 1B)
209    \ef        formfeed (hex 0C)    \ef        formfeed (hex 0C)
210    \en        newline (hex 0A)    \en        linefeed (hex 0A)
211    \er        carriage return (hex 0D)    \er        carriage return (hex 0D)
212    \et        tab (hex 09)    \et        tab (hex 09)
213    \eddd      character with octal code ddd, or backreference    \eddd      character with octal code ddd, or backreference
# Line 164  Thus \ecz becomes hex 1A, but \ec{ becom Line 222  Thus \ecz becomes hex 1A, but \ec{ becom
222  After \ex, from zero to two hexadecimal digits are read (letters can be in  After \ex, from zero to two hexadecimal digits are read (letters can be in
223  upper or lower case). Any number of hexadecimal digits may appear between \ex{  upper or lower case). Any number of hexadecimal digits may appear between \ex{
224  and }, but the value of the character code must be less than 256 in non-UTF-8  and }, but the value of the character code must be less than 256 in non-UTF-8
225  mode, and less than 2**31 in UTF-8 mode (that is, the maximum hexadecimal value  mode, and less than 2**31 in UTF-8 mode. That is, the maximum value in
226  is 7FFFFFFF). If characters other than hexadecimal digits appear between \ex{  hexadecimal is 7FFFFFFF. Note that this is bigger than the largest Unicode code
227  and }, or if there is no terminating }, this form of escape is not recognized.  point, which is 10FFFF.
228  Instead, the initial \ex will be interpreted as a basic hexadecimal escape,  .P
229  with no following digits, giving a character whose value is zero.  If characters other than hexadecimal digits appear between \ex{ and }, or if
230    there is no terminating }, this form of escape is not recognized. Instead, the
231    initial \ex will be interpreted as a basic hexadecimal escape, with no
232    following digits, giving a character whose value is zero.
233  .P  .P
234  Characters whose value is less than 256 can be defined by either of the two  Characters whose value is less than 256 can be defined by either of the two
235  syntaxes for \ex. There is no difference in the way they are handled. For  syntaxes for \ex. There is no difference in the way they are handled. For
# Line 240  meanings Line 301  meanings
301  .SS "Absolute and relative back references"  .SS "Absolute and relative back references"
302  .rs  .rs
303  .sp  .sp
304  The sequence \eg followed by a positive or negative number, optionally enclosed  The sequence \eg followed by an unsigned or a negative number, optionally
305  in braces, is an absolute or relative back reference. A named back reference  enclosed in braces, is an absolute or relative back reference. A named back
306  can be coded as \eg{name}. Back references are discussed  reference can be coded as \eg{name}. Back references are discussed
307  .\" HTML <a href="#backreferences">  .\" HTML <a href="#backreferences">
308  .\" </a>  .\" </a>
309  later,  later,
# Line 254  parenthesized subpatterns. Line 315  parenthesized subpatterns.
315  .\"  .\"
316  .  .
317  .  .
318    .SS "Absolute and relative subroutine calls"
319    .rs
320    .sp
321    For compatibility with Oniguruma, the non-Perl syntax \eg followed by a name or
322    a number enclosed either in angle brackets or single quotes, is an alternative
323    syntax for referencing a subpattern as a "subroutine". Details are discussed
324    .\" HTML <a href="#onigurumasubroutines">
325    .\" </a>
326    later.
327    .\"
328    Note that \eg{...} (Perl syntax) and \eg<...> (Oniguruma syntax) are \fInot\fP
329    synonymous. The former is a back reference; the latter is a subroutine call.
330    .
331    .
332  .SS "Generic character types"  .SS "Generic character types"
333  .rs  .rs
334  .sp  .sp
# Line 343  accented letters, and these are matched Line 418  accented letters, and these are matched
418  is discouraged.  is discouraged.
419  .  .
420  .  .
421    .\" HTML <a name="newlineseq"></a>
422  .SS "Newline sequences"  .SS "Newline sequences"
423  .rs  .rs
424  .sp  .sp
425  Outside a character class, the escape sequence \eR matches any Unicode newline  Outside a character class, by default, the escape sequence \eR matches any
426  sequence. This is a Perl 5.10 feature. In non-UTF-8 mode \eR is equivalent to  Unicode newline sequence. This is a Perl 5.10 feature. In non-UTF-8 mode \eR is
427  the following:  equivalent to the following:
428  .sp  .sp
429    (?>\er\en|\en|\ex0b|\ef|\er|\ex85)    (?>\er\en|\en|\ex0b|\ef|\er|\ex85)
430  .sp  .sp
# Line 368  are added: LS (line separator, U+2028) a Line 444  are added: LS (line separator, U+2028) a
444  Unicode character property support is not needed for these characters to be  Unicode character property support is not needed for these characters to be
445  recognized.  recognized.
446  .P  .P
447    It is possible to restrict \eR to match only CR, LF, or CRLF (instead of the
448    complete set of Unicode line endings) by setting the option PCRE_BSR_ANYCRLF
449    either at compile time or when the pattern is matched. (BSR is an abbrevation
450    for "backslash R".) This can be made the default when PCRE is built; if this is
451    the case, the other behaviour can be requested via the PCRE_BSR_UNICODE option.
452    It is also possible to specify these settings by starting a pattern string with
453    one of the following sequences:
454    .sp
455      (*BSR_ANYCRLF)   CR, LF, or CRLF only
456      (*BSR_UNICODE)   any Unicode newline sequence
457    .sp
458    These override the default and the options given to \fBpcre_compile()\fP, but
459    they can be overridden by options given to \fBpcre_exec()\fP. Note that these
460    special settings, which are not Perl-compatible, are recognized only at the
461    very start of a pattern, and that they must be in upper case. If more than one
462    of them is present, the last one is used. They can be combined with a change of
463    newline convention, for example, a pattern can start with:
464    .sp
465      (*ANY)(*BSR_ANYCRLF)
466    .sp
467  Inside a character class, \eR matches the letter "R".  Inside a character class, \eR matches the letter "R".
468  .  .
469  .  .
# Line 376  Inside a character class, \eR matches th Line 472  Inside a character class, \eR matches th
472  .rs  .rs
473  .sp  .sp
474  When PCRE is built with Unicode character property support, three additional  When PCRE is built with Unicode character property support, three additional
475  escape sequences to match character properties are available when UTF-8 mode  escape sequences that match characters with specific properties are available.
476  is selected. They are:  When not in UTF-8 mode, these sequences are of course limited to testing
477    characters whose codepoints are less than 256, but they do work in this mode.
478    The extra escape sequences are:
479  .sp  .sp
480    \ep{\fIxx\fP}   a character with the \fIxx\fP property    \ep{\fIxx\fP}   a character with the \fIxx\fP property
481    \eP{\fIxx\fP}   a character without the \fIxx\fP property    \eP{\fIxx\fP}   a character without the \fIxx\fP property
# Line 529  The special property L& is also supporte Line 627  The special property L& is also supporte
627  the Lu, Ll, or Lt property, in other words, a letter that is not classified as  the Lu, Ll, or Lt property, in other words, a letter that is not classified as
628  a modifier or "other".  a modifier or "other".
629  .P  .P
630    The Cs (Surrogate) property applies only to characters in the range U+D800 to
631    U+DFFF. Such characters are not valid in UTF-8 strings (see RFC 3629) and so
632    cannot be tested by PCRE, unless UTF-8 validity checking has been turned off
633    (see the discussion of PCRE_NO_UTF8_CHECK in the
634    .\" HREF
635    \fBpcreapi\fP
636    .\"
637    page).
638    .P
639  The long synonyms for these properties that Perl supports (such as \ep{Letter})  The long synonyms for these properties that Perl supports (such as \ep{Letter})
640  are not supported by PCRE, nor is it permitted to prefix any of these  are not supported by PCRE, nor is it permitted to prefix any of these
641  properties with "Is".  properties with "Is".
# Line 553  atomic group Line 660  atomic group
660  (see below).  (see below).
661  .\"  .\"
662  Characters with the "mark" property are typically accents that affect the  Characters with the "mark" property are typically accents that affect the
663  preceding character.  preceding character. None of them have codepoints less than 256, so in
664    non-UTF-8 mode \eX matches any one character.
665  .P  .P
666  Matching characters by Unicode property is not fast, because PCRE has to search  Matching characters by Unicode property is not fast, because PCRE has to search
667  a structure that contains data for over fifteen thousand characters. That is  a structure that contains data for over fifteen thousand characters. That is
# Line 903  alternative in the subpattern. Line 1011  alternative in the subpattern.
1011  .rs  .rs
1012  .sp  .sp
1013  The settings of the PCRE_CASELESS, PCRE_MULTILINE, PCRE_DOTALL, and  The settings of the PCRE_CASELESS, PCRE_MULTILINE, PCRE_DOTALL, and
1014  PCRE_EXTENDED options can be changed from within the pattern by a sequence of  PCRE_EXTENDED options (which are Perl-compatible) can be changed from within
1015  Perl option letters enclosed between "(?" and ")". The option letters are  the pattern by a sequence of Perl option letters enclosed between "(?" and ")".
1016    The option letters are
1017  .sp  .sp
1018    i  for PCRE_CASELESS    i  for PCRE_CASELESS
1019    m  for PCRE_MULTILINE    m  for PCRE_MULTILINE
# Line 918  PCRE_MULTILINE while unsetting PCRE_DOTA Line 1027  PCRE_MULTILINE while unsetting PCRE_DOTA
1027  permitted. If a letter appears both before and after the hyphen, the option is  permitted. If a letter appears both before and after the hyphen, the option is
1028  unset.  unset.
1029  .P  .P
1030    The PCRE-specific options PCRE_DUPNAMES, PCRE_UNGREEDY, and PCRE_EXTRA can be
1031    changed in the same way as the Perl-compatible options by using the characters
1032    J, U and X respectively.
1033    .P
1034  When an option change occurs at top level (that is, not inside subpattern  When an option change occurs at top level (that is, not inside subpattern
1035  parentheses), the change applies to the remainder of the pattern that follows.  parentheses), the change applies to the remainder of the pattern that follows.
1036  If the change is placed right at the start of a pattern, PCRE extracts it into  If the change is placed right at the start of a pattern, PCRE extracts it into
# Line 941  branch is abandoned before the option se Line 1054  branch is abandoned before the option se
1054  option settings happen at compile time. There would be some very weird  option settings happen at compile time. There would be some very weird
1055  behaviour otherwise.  behaviour otherwise.
1056  .P  .P
1057  The PCRE-specific options PCRE_DUPNAMES, PCRE_UNGREEDY, and PCRE_EXTRA can be  \fBNote:\fP There are other PCRE-specific options that can be set by the
1058  changed in the same way as the Perl-compatible options by using the characters  application when the compile or match functions are called. In some cases the
1059  J, U and X respectively.  pattern can contain special leading sequences to override what the application
1060    has set or what has been defaulted. Details are given in the section entitled
1061    .\" HTML <a href="#newlineseq">
1062    .\" </a>
1063    "Newline sequences"
1064    .\"
1065    above.
1066  .  .
1067  .  .
1068  .\" HTML <a name="subpattern"></a>  .\" HTML <a name="subpattern"></a>
# Line 1092  details of the interfaces for handling n Line 1211  details of the interfaces for handling n
1211  \fBpcreapi\fP  \fBpcreapi\fP
1212  .\"  .\"
1213  documentation.  documentation.
1214    .P
1215    \fBWarning:\fP You cannot use different names to distinguish between two
1216    subpatterns with the same number (see the previous section) because PCRE uses
1217    only the numbers when matching.
1218  .  .
1219  .  .
1220  .SH REPETITION  .SH REPETITION
# Line 1140  support is available, \eX{3} matches thr Line 1263  support is available, \eX{3} matches thr
1263  which may be several bytes long (and they may be of different lengths).  which may be several bytes long (and they may be of different lengths).
1264  .P  .P
1265  The quantifier {0} is permitted, causing the expression to behave as if the  The quantifier {0} is permitted, causing the expression to behave as if the
1266  previous item and the quantifier were not present.  previous item and the quantifier were not present. This may be useful for
1267    subpatterns that are referenced as
1268    .\" HTML <a href="#subpatternsassubroutines">
1269    .\" </a>
1270    subroutines
1271    .\"
1272    from elsewhere in the pattern. Items other than subpatterns that have a {0}
1273    quantifier are omitted from the compiled pattern.
1274  .P  .P
1275  For convenience, the three most common quantifiers have single-character  For convenience, the three most common quantifiers have single-character
1276  abbreviations:  abbreviations:
# Line 1287  previous example can be rewritten as Line 1417  previous example can be rewritten as
1417  .sp  .sp
1418    \ed++foo    \ed++foo
1419  .sp  .sp
1420    Note that a possessive quantifier can be used with an entire group, for
1421    example:
1422    .sp
1423      (abc|xyz){2,3}+
1424    .sp
1425  Possessive quantifiers are always greedy; the setting of the PCRE_UNGREEDY  Possessive quantifiers are always greedy; the setting of the PCRE_UNGREEDY
1426  option is ignored. They are a convenient notation for the simpler forms of  option is ignored. They are a convenient notation for the simpler forms of
1427  atomic group. However, there is no difference in the meaning of a possessive  atomic group. However, there is no difference in the meaning of a possessive
# Line 1361  subpattern is possible using named paren Line 1496  subpattern is possible using named paren
1496  .P  .P
1497  Another way of avoiding the ambiguity inherent in the use of digits following a  Another way of avoiding the ambiguity inherent in the use of digits following a
1498  backslash is to use the \eg escape sequence, which is a feature introduced in  backslash is to use the \eg escape sequence, which is a feature introduced in
1499  Perl 5.10. This escape must be followed by a positive or a negative number,  Perl 5.10. This escape must be followed by an unsigned number or a negative
1500  optionally enclosed in braces. These examples are all identical:  number, optionally enclosed in braces. These examples are all identical:
1501  .sp  .sp
1502    (ring), \e1    (ring), \e1
1503    (ring), \eg1    (ring), \eg1
1504    (ring), \eg{1}    (ring), \eg{1}
1505  .sp  .sp
1506  A positive number specifies an absolute reference without the ambiguity that is  An unsigned number specifies an absolute reference without the ambiguity that
1507  present in the older syntax. It is also useful when literal digits follow the  is present in the older syntax. It is also useful when literal digits follow
1508  reference. A negative number is a relative reference. Consider this example:  the reference. A negative number is a relative reference. Consider this
1509    example:
1510  .sp  .sp
1511    (abc(def)ghi)\eg{-1}    (abc(def)ghi)\eg{-1}
1512  .sp  .sp
# Line 1917  It matches "abcabc". It does not match " Line 2053  It matches "abcabc". It does not match "
2053  processing option does not affect the called subpattern.  processing option does not affect the called subpattern.
2054  .  .
2055  .  .
2056    .\" HTML <a name="onigurumasubroutines"></a>
2057    .SH "ONIGURUMA SUBROUTINE SYNTAX"
2058    .rs
2059    .sp
2060    For compatibility with Oniguruma, the non-Perl syntax \eg followed by a name or
2061    a number enclosed either in angle brackets or single quotes, is an alternative
2062    syntax for referencing a subpattern as a subroutine, possibly recursively. Here
2063    are two of the examples used above, rewritten using this syntax:
2064    .sp
2065      (?<pn> \e( ( (?>[^()]+) | \eg<pn> )* \e) )
2066      (sens|respons)e and \eg'1'ibility
2067    .sp
2068    PCRE supports an extension to Oniguruma: if a number is preceded by a
2069    plus or a minus sign it is taken as a relative reference. For example:
2070    .sp
2071      (abc)(?i:\eg<-1>)
2072    .sp
2073    Note that \eg{...} (Perl syntax) and \eg<...> (Oniguruma syntax) are \fInot\fP
2074    synonymous. The former is a back reference; the latter is a subroutine call.
2075    .
2076    .
2077  .SH CALLOUTS  .SH CALLOUTS
2078  .rs  .rs
2079  .sp  .sp
# Line 1953  description of the interface to the call Line 2110  description of the interface to the call
2110  documentation.  documentation.
2111  .  .
2112  .  .
2113    .SH "BACKTRACKING CONTROL"
2114    .rs
2115    .sp
2116    Perl 5.10 introduced a number of "Special Backtracking Control Verbs", which
2117    are described in the Perl documentation as "experimental and subject to change
2118    or removal in a future version of Perl". It goes on to say: "Their usage in
2119    production code should be noted to avoid problems during upgrades." The same
2120    remarks apply to the PCRE features described in this section.
2121    .P
2122    Since these verbs are specifically related to backtracking, most of them can be
2123    used only when the pattern is to be matched using \fBpcre_exec()\fP, which uses
2124    a backtracking algorithm. With the exception of (*FAIL), which behaves like a
2125    failing negative assertion, they cause an error if encountered by
2126    \fBpcre_dfa_exec()\fP.
2127    .P
2128    The new verbs make use of what was previously invalid syntax: an opening
2129    parenthesis followed by an asterisk. In Perl, they are generally of the form
2130    (*VERB:ARG) but PCRE does not support the use of arguments, so its general
2131    form is just (*VERB). Any number of these verbs may occur in a pattern. There
2132    are two kinds:
2133    .
2134    .SS "Verbs that act immediately"
2135    .rs
2136    .sp
2137    The following verbs act as soon as they are encountered:
2138    .sp
2139       (*ACCEPT)
2140    .sp
2141    This verb causes the match to end successfully, skipping the remainder of the
2142    pattern. When inside a recursion, only the innermost pattern is ended
2143    immediately. PCRE differs from Perl in what happens if the (*ACCEPT) is inside
2144    capturing parentheses. In Perl, the data so far is captured: in PCRE no data is
2145    captured. For example:
2146    .sp
2147      A(A|B(*ACCEPT)|C)D
2148    .sp
2149    This matches "AB", "AAD", or "ACD", but when it matches "AB", no data is
2150    captured.
2151    .sp
2152      (*FAIL) or (*F)
2153    .sp
2154    This verb causes the match to fail, forcing backtracking to occur. It is
2155    equivalent to (?!) but easier to read. The Perl documentation notes that it is
2156    probably useful only when combined with (?{}) or (??{}). Those are, of course,
2157    Perl features that are not present in PCRE. The nearest equivalent is the
2158    callout feature, as for example in this pattern:
2159    .sp
2160      a+(?C)(*FAIL)
2161    .sp
2162    A match with the string "aaaa" always fails, but the callout is taken before
2163    each backtrack happens (in this example, 10 times).
2164    .
2165    .SS "Verbs that act after backtracking"
2166    .rs
2167    .sp
2168    The following verbs do nothing when they are encountered. Matching continues
2169    with what follows, but if there is no subsequent match, a failure is forced.
2170    The verbs differ in exactly what kind of failure occurs.
2171    .sp
2172      (*COMMIT)
2173    .sp
2174    This verb causes the whole match to fail outright if the rest of the pattern
2175    does not match. Even if the pattern is unanchored, no further attempts to find
2176    a match by advancing the start point take place. Once (*COMMIT) has been
2177    passed, \fBpcre_exec()\fP is committed to finding a match at the current
2178    starting point, or not at all. For example:
2179    .sp
2180      a+(*COMMIT)b
2181    .sp
2182    This matches "xxaab" but not "aacaab". It can be thought of as a kind of
2183    dynamic anchor, or "I've started, so I must finish."
2184    .sp
2185      (*PRUNE)
2186    .sp
2187    This verb causes the match to fail at the current position if the rest of the
2188    pattern does not match. If the pattern is unanchored, the normal "bumpalong"
2189    advance to the next starting character then happens. Backtracking can occur as
2190    usual to the left of (*PRUNE), or when matching to the right of (*PRUNE), but
2191    if there is no match to the right, backtracking cannot cross (*PRUNE).
2192    In simple cases, the use of (*PRUNE) is just an alternative to an atomic
2193    group or possessive quantifier, but there are some uses of (*PRUNE) that cannot
2194    be expressed in any other way.
2195    .sp
2196      (*SKIP)
2197    .sp
2198    This verb is like (*PRUNE), except that if the pattern is unanchored, the
2199    "bumpalong" advance is not to the next character, but to the position in the
2200    subject where (*SKIP) was encountered. (*SKIP) signifies that whatever text
2201    was matched leading up to it cannot be part of a successful match. Consider:
2202    .sp
2203      a+(*SKIP)b
2204    .sp
2205    If the subject is "aaaac...", after the first match attempt fails (starting at
2206    the first character in the string), the starting point skips on to start the
2207    next attempt at "c". Note that a possessive quantifer does not have the same
2208    effect in this example; although it would suppress backtracking during the
2209    first match attempt, the second attempt would start at the second character
2210    instead of skipping on to "c".
2211    .sp
2212      (*THEN)
2213    .sp
2214    This verb causes a skip to the next alternation if the rest of the pattern does
2215    not match. That is, it cancels pending backtracking, but only within the
2216    current alternation. Its name comes from the observation that it can be used
2217    for a pattern-based if-then-else block:
2218    .sp
2219      ( COND1 (*THEN) FOO | COND2 (*THEN) BAR | COND3 (*THEN) BAZ ) ...
2220    .sp
2221    If the COND1 pattern matches, FOO is tried (and possibly further items after
2222    the end of the group if FOO succeeds); on failure the matcher skips to the
2223    second alternative and tries COND2, without backtracking into COND1. If (*THEN)
2224    is used outside of any alternation, it acts exactly like (*PRUNE).
2225    .
2226    .
2227  .SH "SEE ALSO"  .SH "SEE ALSO"
2228  .rs  .rs
2229  .sp  .sp
# Line 1973  Cambridge CB2 3QH, England. Line 2244  Cambridge CB2 3QH, England.
2244  .rs  .rs
2245  .sp  .sp
2246  .nf  .nf
2247  Last updated: 13 June 2007  Last updated: 08 March 2009
2248  Copyright (c) 1997-2007 University of Cambridge.  Copyright (c) 1997-2009 University of Cambridge.
2249  .fi  .fi

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