1Pod::Abstract::Path(3)User Contributed Perl DocumentationPod::Abstract::Path(3)
2
6 Pod::Abstract::Path - Search for POD nodes matching a path within a
7 document tree.
8
10 /head1(1)/head2 # All head2 elements under
11 # the 2nd head1 element
12 //item # All items anywhere
13 //item[@label =~ {^\*$}] # All items with '*' labels.
14 //head2[/hilight] # All head2 elements containing
15 # "hilight" elements
16 # Top level head1s containing head2s that have headings matching
18 # "NAME", and also have at least one list somewhere in their
19 # contents.
20 /head1[/head2[@heading =~ {NAME}]][//over]
21 # Top level headings having the same title as the following heading.
23 /head1[@heading = >>@heading]
24 # Top level headings containing at least one subheading with the same
26 # name.
27 /head1[@heading = ./head2@heading]
28
30 Pod::Abstract::Path is a path selection syntax that allows fast and
31 easy traversal of Pod::Abstract documents. While it has a simple
32 syntax, there is significant complexity in the queries that you can
33 create.
34 Not all of the designed features have yet been implemented, but it is
36 currently quite useful, and all of the filters in "paf" make use of Pod
37 Paths.
38 SYMBOLS:
40 / Selects children of the left hand side.
41 // Selects all descendants of the left hand side.
43 . Selects the current node - this is a NOP that can be used in
45 expressions.
46 .. Selects the parrent node. If there are multiple nodes selected, all
48 of their parents will be included.
49 ^ Selects the root node of the tree for the current node. This allows
51 you to escape from a nested expression. Note that this is the ROOT
52 node, not the node that you started from.
53 If you want to evaluate an expression from a node as though it were
55 the root node, the easiest ways are to detach or dup it - otherwise
56 the root operator will find the original root node.
57 name, #cut, :text, :verbatim, :paragraph
59 Any element name, or symbolic type name, will restrict the
60 selection to only elements matching that type. e.g,
61 ""//:paragraph"" will select all descendants, anywhere, but then
62 restrict that set to only ":paragraph" type nodes.
63 Names together separated by spaces will match all of those names -
65 e.g: "//head1 over" will match all lists and all head1s.
66 &, | (union and intersection)
68 Union will take expressions on either side, and return all nodes
69 that are members of either set. Intersection returns nodes that are
70 members of BOTH sets. These can be used to extend expressions, and
71 within [ expressions ] where a path is supported (left side of a
72 match, left or right side of an = sign). These are NOT logical
73 and/or, though a similar effect can be induced through these
74 operators.
75 @attrname
77 The named attribute of the nodes on the left hand side. Current
78 attributes are @heading for head1 through head4, and @label for
79 list items.
80 [ expression ]
82 Select only the left hand elements that match the expression in the
83 brackets. The expression will be evaluated from the point of view
84 of each node in the current result set.
85 Expressions can be:
87 simple: "[/head2]"
89 Any regular path will be true if there are any nodes matched.
90 The above example will be true if there are any head2 nodes as
91 direct children of the selected node.
92 regex match: "[@heading =~ {FOO}]"
94 A regex match will be true if the left hand expression has
95 nodes that match the regular expression between the braces on
96 the right hand side. The above example will match anything with
97 a heading containing "FOO".
98 Optionally, the right hand closing brace may have the "i"
100 modifier to cause case-insensitive matching. i.e "[@heading =~
101 {foo}i]" will match "foo" or "fOO".
102 complement: "[! /head2 ]"
104 Reverses the remainder of the expression. The above example
105 will match anything without a child head2 node.
106 compare operators: eg. "[ /node1 eq /node2 ]"
108 Matches nodes where the operator is satistied for at least one
109 pair of nodes. The right hand expression can be a constant
110 string (single quoted: 'string', or a second expression. If two
111 expressions are used, they are matched combinationally - i.e,
112 all result nodes on the left are matched against all result
113 nodes on the right. Both sides may contain nested expressions.
114 The following Perl compatible operators are supported:
116 String: " eq gt lt le ge ne "
118 Numeric: "== < > <= >= !="
120
122 Pod::Abstract::Path is not designed to be fast. It is designed to be
123 expressive and useful, but it involves sucessive
124 expand/de-duplicate/linear search operations and doing this with large
125 documents containing many nodes is not suitable for high performance
126 systems.
127 Simple expressions can be fast enough, but there is nothing to stop you
129 from writing "//[<condition>]" and linear-searching all 10,000 nodes of
130 your Pod document. Use with caution in interactive systems.
131
133 It is recommended you use the "<Pod::Abstract::Node-"select>> method to
134 evaluate Path expressions.
135 If you wish to generate paths for use in other modules, use
137 "parse_path" to generate a parse tree, pass that as an argument to
138 "new", then use "process" to evaluate the expression against a list of
139 nodes. You can re-use the same parse tree to process multiple lists of
140 nodes in this fashion.
141
143 filter_unique
144 It is possible during processing - especially using ^ or .. operators -
145 to generate many duplicate matches of the same nodes. Each pass around
146 the loop, we filter to unique nodes so that duplicates cannot inflate
147 more than one time.
148 This effectively means that "//^" (however awful that is) will match
150 one node only - just really inefficiently.
151 parse_path
153 Parse a list of lexemes and generate a driver tree for the process
154 method. This is a simple recursive descent parser with one element of
155 lookahead.
156
158 Ben Lilburne <bnej@mac.com>
159
161 Copyright (C) 2009 Ben Lilburne
162 This program is free software; you can redistribute it and/or modify it
164 under the same terms as Perl itself.
165perl v5.30.0 2019-07-26 Pod::Abstract::Path(3)