Mercurial > hg > xemacs-beta

comparison etc/ETAGS.EBNF @ 2225:4968c73cb252

Find changesets by keywords (author, files, the commit message), revision number or hash, or revset expression.
[xemacs-hg @ 2004-08-20 04:40:08 by james] Update to etags.c version 16.56.
author james
date Fri, 20 Aug 2004 04:40:11 +0000
parents
children 9d8bfee6e672
comparison
equal deleted inserted replaced
2224:6e8a6fd7d08b 2225:4968c73cb252
1 -*- indented-text -*-
2
3 This file contains two sections:
4
5 1) An EBNF (Extended Backus Normal Form) description of the format of
6 the tags file created by etags.c and interpreted by etags.el;
7 2) A discussion of tag names and implicit tag names.
8
9 ====================== 1) EBNF tag file description =====================
10
11 Productions created from current behaviour to aid extensions
12 Francesco Potorti` <pot@gnu.org> 2002
13 ----------------
14
15 FF ::= #x0c /* tag section starter */
16
17 LF ::= #x0a /* line terminator */
18
19 DEL ::= #x7f /* pattern terminator */
20
21 SOH ::= #x01 /* name terminator */
22
23 regchar ::= [^#x0a#x0c#x7f] /* regular character */
24
25 regstring ::= { regchar } /* regular string */
26
27 unsint ::= [0-9] { [0-9] } /* non-negative integer */
28
29
30
31 tagfile ::= { tagsection } /* a tags file */
32
33 tagsection ::= FF LF ( includesec | regularsec ) LF
34
35 includesec ::= filename ",include" [ LF fileprop ]
36
37 regularsec ::= filename "," [ unsint ] [ LF fileprop ] { LF tag }
38
39 filename ::= regchar regstring /* a file name */
40
41 fileprop ::= "(" regstring ")" /* an elisp alist */
42
43 tag ::= directtag | patterntag
44
45 directtag ::= DEL realposition /* no pattern */
46
47 patterntag ::= pattern DEL [ tagname SOH ] position
48
49 pattern ::= regstring /* a tag pattern */
50
51 tagname ::= regchar regstring /* a tag name */
52
53 position ::= realposition | "," /* charpos,linepos */
54
55 realposition ::= "," unsint | unsint "," | unsint "," unsint
56
57 ==================== end of EBNF tag file description ====================
58
59
60
61 ======================= 2) discussion of tag names =======================
62
63 - WHAT ARE TAG NAMES
64 Tag lines in a tags file are usually made from the above defined pattern
65 and by an optional tag name. The pattern is a string that is searched
66 in the source file to find the tagged line.
67
68 - WHY TAG NAMES ARE GOOD
69 When a user looks for a tag, Emacs first compares the tag with the tag
70 names contained in the tags file. If no match is found, Emacs compares
71 the tag with the patterns. The tag name is then the preferred way to
72 look for tags in the tags file, because when the tag name is present
73 Emacs can find a tag faster and more accurately. These tag names are
74 part of tag lines in the tags file, so we call them "explicit".
75
76 - WHY IMPLICIT TAG NAMES ARE EVEN BETTER
77 When a tag line has no name, but a name can be deduced from the pattern,
78 we say that the tag line has an implicit tag name. Often tag names are
79 redundant; this happens when the name of a tag is an easily guessable
80 substring of the tag pattern. We define a set of rules to decide
81 whether it is possible to deduce the tag name from the pattern, and make
82 an unnamed tag in those cases. The name deduced from the pattern of an
83 unnamed tag is the implicit name of that tag.
84 When the user looks for a tag, and Emacs founds no explicit tag names
85 that match it, Emacs then looks for an tag whose implicit tag name
86 matches the request. etags.c uses implicit tag names when possible, in
87 order to reduce the size of the tags file.
88 An implicit tag name is deduced from the pattern by discarding the
89 last character if it is one of ` \f\t\n\r()=,;', then taking all the
90 rightmost consecutive characters in the pattern which are not one of
91 those.
92
93 ===================== end of discussion of tag names =====================