The TS file format used by Qt Linguist is described by the DTD presented below, which we include for your convenience. Be aware that the format may change in future Qt releases.

<!--
 !
 ! Some notes to the DTD:
 !
 ! The location element is set as optional since it was introduced first in Qt 4.2.
 ! The userdata element is set as optional since it was introduced first in Qt 4.4.
 ! The vanished message type was introduced first in Qt 5.2.
 !
  -->
<!--
 ! Macro used in order to escape byte entities not allowed in an xml document
 ! for instance, only #x9, #xA and #xD are allowed characters below #x20.
 -->
<!ENTITY % evilstring '(#PCDATA | byte)*' >
<!ELEMENT byte EMPTY>
<!-- value contains decimal (e.g. 1000) or hex (e.g. x3e8) unicode encoding of one char -->
<!ATTLIST byte
          value CDATA #REQUIRED>
<!--
 ! This element wildcard is no valid DTD. No better solution available.
 ! extra elements may appear in TS and message elements. Each element may appear
 ! only once within each scope. The contents are preserved verbatim; any
 ! attributes are dropped. Currently recognized extra tags include:
 !   extra-po-msgid_plural, extra-po-old_msgid_plural
 !   extra-po-flags (comma-space separated list)
 !   extra-loc-layout_id
 !   extra-loc-feature
 !   extra-loc-blank
  -->
<!ELEMENT extra-* %evilstring; >
<!ELEMENT TS (defaultcodec?, extra-**, dependencies?, (context|message)+) >
<!ATTLIST TS
          version CDATA #IMPLIED
          sourcelanguage CDATA #IMPLIED
          language CDATA #IMPLIED>
<!-- The encoding to use in the QM file by default. Default is ISO-8859-1. -->
<!ELEMENT defaultcodec (#PCDATA) >
<!ELEMENT context (name, comment?, (context|message)+) >
<!ATTLIST context
          encoding CDATA #IMPLIED>
<!ELEMENT dependencies (dependency+) >
<!ATTLIST dependency
          catalog CDATA #IMPLIED>
<!ELEMENT name %evilstring; >
<!-- This is "disambiguation" in the (new) API, or "msgctxt" in gettext speak -->
<!ELEMENT comment %evilstring; >
<!-- Previous content of comment (result of merge) -->
<!ELEMENT oldcomment %evilstring; >
<!-- The real comment (added by developer/designer) -->
<!ELEMENT extracomment %evilstring; >
<!-- Comment added by translator -->
<!ELEMENT translatorcomment %evilstring; >
<!ELEMENT message (location*, source?, oldsource?, comment?, oldcomment?, extracomment?, translatorcomment?, translation?, userdata?, extra-**) >
<!--
 ! If utf8 is "true", the defaultcodec is overridden and the message is encoded
 ! in UTF-8 in the QM file. If it is "both", both source encodings are stored
 ! in the QM file.
  -->
<!ATTLIST message
          id CDATA #IMPLIED
          utf8 (true|false|both) "false"
          numerus (yes|no) "no">
<!ELEMENT location EMPTY>
<!--
 ! If the line is omitted, the location specifies only a file.
 !
 ! location supports relative specifications as well. Line numbers are
 ! relative (explicitly positive or negative) to the last reference to a
 ! given filename; each file starts with current line 0. If the filename
 ! is omitted, the "current" one is used. For the 1st location in a message,
 ! "current" is the filename used for the 1st location of the previous message.
 ! For subsequent locations, it is the filename used for the previous location.
 ! A single TS file has either all absolute or all relative locations.
  -->
<!ATTLIST location
          filename CDATA #IMPLIED
          line CDATA #IMPLIED>
<!ELEMENT source %evilstring;>
<!-- Previous content of source (result of merge) -->
<!ELEMENT oldsource %evilstring;>
<!--
 ! The following should really say one evilstring macro or several
 ! numerusform or lengthvariant elements, but the DTD can't express this.
  -->
<!ELEMENT translation (#PCDATA|byte|numerusform|lengthvariant)* >
<!--
 ! If no type is set, the message is "finished".
 ! Length variants must be ordered by falling display length.
 ! variants may not be yes if the message has numerus yes.
  -->
<!ATTLIST translation
          type (unfinished|vanished|obsolete) #IMPLIED
          variants (yes|no) "no">
<!-- Deprecated. Use extra-* -->
<!ELEMENT userdata (#PCDATA)* >
<!--
 ! The following should really say one evilstring macro or several
 ! lengthvariant elements, but the DTD can't express this.
 ! Length variants must be ordered by falling display length.
  -->
<!ELEMENT numerusform (#PCDATA|byte|lengthvariant)* >
<!ATTLIST numerusform
          variants (yes|no) "no">
<!ELEMENT lengthvariant %evilstring; >