/[emacs]/emacs/etc/ETAGS.EBNF
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revision 1.6 by pot, Tue Jul 2 11:35:27 2002 UTC revision 1.7 by pot, Tue Jul 2 11:54:32 2002 UTC
# Line 1  Line 1 
1    -*- indented-text -*-
2    
3  This file contains two sections:  This file contains two sections:
4    
5  1) An EBNF (Extended Backus Normal Form) description of the format of  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     the tags file created by etags.c and interpreted by etags.el
7  2) A discussion of tag names and implicit tag names  2) A discussion of tag names and implicit tag names
8    
9  ======================= EBNF tag file description =======================  ======================= EBNF tag file description =======================
# Line 56  realposition ::= "," unsint | unsint "," Line 58  realposition ::= "," unsint | unsint ","
58    
59    
60    
61  ======================== discussion on tag names =========================  ======================== discussion of tag names =========================
62    
63  - What are tag names  - What are tag names
64  Tag lines in a tags file are usually made from the above defined pattern  Tag lines in a tags file are usually made from the above defined pattern
# Line 72  Emacs can find a tag faster and more acc Line 74  Emacs can find a tag faster and more acc
74  part of tag lines in the tags file, so we call them "explicit".  part of tag lines in the tags file, so we call them "explicit".
75    
76  - Why implicit tag names are even better  - Why implicit tag names are even better
77  Often tag names are redundant; this happens when the name of a tag is an  When a tag line has no name, but a name can be deduced from the pattern,
78  easily guessable substring of the tag pattern.  We define a set of rules  we say that the tag line has an implicit tag name.  etags.c uses
79  to decide whether it is possible to deduce the tag name from the pattern,  implicit tag names when possible, in order to reduce the number of
80  and make an unnamed tag in those cases.  The name deduced from the  explicit tag names in a tags file, thus reducing the size of the tags
81  pattern of an unnamed tag is the implicit name of that tag.  The use of  file.  When the user looks for a tag, and Emacs founds no explicit tag
82  implicit tag names reduces the size of the tags file.  When the user  names that match it, Emacs then tries to match the tag with an implicit
83  looks for a tag, and Emacs founds no explicit tag names that match it,  tag name.  Such a match occurs when the tag matches a pattern, subject
84  Emacs then tries to match the tag with an implicit tag name.  Such a  to the satisfaction of all the following four rules:
 match occurs when the tag matches a pattern, subject to the satisfaction  
 of all the following four rules:  
85    
86   NONAM=" \f\t\n\r()=,;";   NONAM=" \f\t\n\r()=,;";
87    1. the tag does not contain any of the characters in NONAM;    1. the tag does not contain any of the characters in NONAM;

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