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Marking translatable strings in an XML file is done through a separate
"rule" file, making use of the Internationalization Tag Set standard
(ITS, https://www.w3.org/TR/its20/). The currently supported ITS
data categories are: ‘Translate’, ‘Localization Note’,
‘Elements Within Text’, and ‘Preserve Space’. In addition to
them, xgettext
also recognizes the following extended data
categories:
This data category associates msgctxt
to the extracted text. In
the global rule, the contextRule
element contains the following:
selector
attribute. It contains an absolute selector
that selects the nodes to which this rule applies.
contextPointer
attribute that contains a relative
selector pointing to a node that holds the msgctxt
value.
textPointer
attribute that contains a relative
selector pointing to a node that holds the msgid
value.
This data category indicates whether the special XML characters
(<
, >
, &
, "
) are escaped with entity
reference. In the global rule, the escapeRule
element contains
the following:
selector
attribute. It contains an absolute selector
that selects the nodes to which this rule applies.
escape
attribute with the value yes
or no
.
This data category extends the standard ‘Preserve Space’ data
category with the additional values ‘trim’ and ‘paragraph’.
‘trim’ means to remove the leading and trailing whitespaces of the
content, but not to normalize whitespaces in the middle.
‘paragraph’ means to normalize the content but keep the paragraph
boundaries. In the global
rule, the preserveSpaceRule
element contains the following:
selector
attribute. It contains an absolute selector
that selects the nodes to which this rule applies.
space
attribute with the value default
,
preserve
, trim
, or paragraph
.
All those extended data categories can only be expressed with global
rules, and the rule elements have to have the
https://www.gnu.org/s/gettext/ns/its/extensions/1.0
namespace.
Given the following XML document in a file messages.xml:
<?xml version="1.0"?> <messages> <message> <p>A translatable string</p> </message> <message> <p translatable="no">A non-translatable string</p> </message> </messages>
To extract the first text content ("A translatable string"), but not the second ("A non-translatable string"), the following ITS rules can be used:
<?xml version="1.0"?> <its:rules xmlns:its="http://www.w3.org/2005/11/its" version="1.0"> <its:translateRule selector="/messages" translate="no"/> <its:translateRule selector="//message/p" translate="yes"/> <!-- If 'p' has an attribute 'translatable' with the value 'no', then the content is not translatable. --> <its:translateRule selector="//message/p[@translatable = 'no']" translate="no"/> </its:rules>
‘xgettext’ needs another file called "locating rule" to associate an ITS rule with an XML file. If the above ITS file is saved as messages.its, the locating rule would look like:
<?xml version="1.0"?> <locatingRules> <locatingRule name="Messages" pattern="*.xml"> <documentRule localName="messages" target="messages.its"/> </locatingRule> <locatingRule name="Messages" pattern="*.msg" target="messages.its"/> </locatingRules>
The locatingRule
element must have a pattern
attribute,
which denotes either a literal file name or a wildcard pattern of the
XML file7. The locatingRule
element can have child
documentRule
element, which adds checks on the content of the XML
file.
The first rule matches any file with the .xml file extension, but it only applies to XML files whose root element is ‘<messages>’.
The second rule indicates that the same ITS rule file are also
applicable to any file with the .msg file extension. The
optional name
attribute of locatingRule
allows to choose
rules by name, typically with xgettext
’s -L
option.
The associated ITS rule file is indicated by the target
attribute
of locatingRule
or documentRule
. If it is specified in a
documentRule
element, the parent locatingRule
shouldn’t
have the target
attribute.
Locating rule files must have the .loc file extension. Both ITS
rule files and locating rule files must be installed in the
$prefix/share/gettext/its directory. Once those files are
properly installed, xgettext
can extract translatable strings
from the matching XML files.
For XML, there are two use-cases of translated strings. One is the case where the translated strings are directly consumed by programs, and the other is the case where the translated strings are merged back to the original XML document. In the former case, special characters in the extracted strings shouldn’t be escaped, while they should in the latter case. To control wheter to escape special characters, the ‘Escape Special Characters’ data category can be used.
To merge the translations, the ‘msgfmt’ program can be used with
the option --xml
. See Invoking the msgfmt
Program, for more details
about how one calls the ‘msgfmt’ program. ‘msgfmt’’s
--xml
option doesn’t perform character escaping, so translated
strings can have arbitrary XML constructs, such as elements for markup.
Note that the file name matching is done after
removing any .in
suffix from the input file name. Thus the
pattern
attribute must not include a pattern matching .in
.
For example, if the input file name is foo.msg.in, the pattern
should be either *.msg
or just *
, rather than
*.in
.