+-*- indented-text -*-
+
+See the end of this file for copyright information.
+
This file contains two sections:
-1) An EBNF (Extended Backus Normal Form) description of the format of
- the tags file created by etags.c and interpreted by etags.el
-2) A discussion of tag names and implicit tag names
+1) An EBNF (Extended Backus-Naur Form) description of the format of
+ the tags file created by etags.c and interpreted by etags.el;
+2) A discussion of tag names and implicit tag names.
-======================= EBNF tag file description =======================
+====================== 1) EBNF tag file description =====================
-Productions created from current behaviour to aid extensions
+Productions created from current behavior to aid extensions
Francesco Potorti` <pot@gnu.org> 2002
----------------
-======================== discussion on tag names =========================
+======================= 2) discussion of tag names =======================
-- What are tag names
+- WHAT ARE TAG NAMES
Tag lines in a tags file are usually made from the above defined pattern
and by an optional tag name. The pattern is a string that is searched
in the source file to find the tagged line.
-- Why tag names are good
+- WHY TAG NAMES ARE GOOD
When a user looks for a tag, Emacs first compares the tag with the tag
names contained in the tags file. If no match is found, Emacs compares
the tag with the patterns. The tag name is then the preferred way to
Emacs can find a tag faster and more accurately. These tag names are
part of tag lines in the tags file, so we call them "explicit".
-- Why implicit tag names are even better
-Often tag names are redundant; this happens when the name of a tag is an
-easily guessable substring of the tag pattern. We define a set of rules
-to decide whether it is possible to deduce the tag name from the pattern,
-and make an unnamed tag in those cases. The name deduced from the
-pattern of an unnamed tag is the implicit name of that tag. The use of
-implicit tag names reduces the size of the tags file. When the user
-looks for a tag, and Emacs founds no explicit tag names that match it,
-Emacs then tries to match the tag with an implicit tag name. Such a
-match occurs when the tag matches a pattern, subject to the satisfaction
-of all the following four rules:
-
- NONAM=" \f\t\n\r()=,;";
- 1. the tag does not contain any of the characters in NONAM;
- 2. the pattern contains the tag as either a rightmost, or rightmost
- but one character, substring;
- 3. the character, if any, immediately before the tag in the pattern
- must be a character in NONAM;
- 4. the character, if any, immediately after the tag in the pattern
- must also be a character in NONAM.
-
-===================== end of discussion on tag names =====================
+- WHY IMPLICIT TAG NAMES ARE EVEN BETTER
+When a tag line has no name, but a name can be deduced from the pattern,
+we say that the tag line has an implicit tag name. Often tag names are
+redundant; this happens when the name of a tag is an easily guessable
+substring of the tag pattern. We define a set of rules to decide
+whether it is possible to deduce the tag name from the pattern, and make
+an unnamed tag in those cases. The name deduced from the pattern of an
+unnamed tag is the implicit name of that tag.
+ When the user looks for a tag, and Emacs finds no explicit tag names
+that match it, Emacs then looks for an tag whose implicit tag name
+matches the request. etags.c uses implicit tag names when possible, in
+order to reduce the size of the tags file.
+ An implicit tag name is deduced from the pattern by discarding the
+last character if it is one of ` \f\t\n\r()=,;', then taking all the
+rightmost consecutive characters in the pattern which are not one of
+those.
+
+===================== end of discussion of tag names =====================
+
+Copyright (C) 2002-2012 Free Software Foundation, Inc.
+
+COPYING PERMISSIONS:
+
+ This document is free software: you can redistribute it and/or modify
+ it under the terms of the GNU General Public License as published by
+ the Free Software Foundation, either version 3 of the License, or
+ (at your option) any later version.
+
+ This program is distributed in the hope that it will be useful,
+ but WITHOUT ANY WARRANTY; without even the implied warranty of
+ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ GNU General Public License for more details.
+
+ You should have received a copy of the GNU General Public License
+ along with this program. If not, see <http://www.gnu.org/licenses/>.
HCoop / bpt / emacs.git / blobdiff