The source XML files
Located in the <MIME>/packages directory,
these XML files provide all the information regarding MIME types that is
installed into the database by the
update-mime-database application. There are a
few rules about the XML file itself:
It must specify the namespace as
“https://www.freedesktop.org/standards/shared-mime-info”
The root element must be mime-info
Zero or more mime-type elements can be
specified as children of the mime-info element. The
type attribute is used to specify the MIME type
that is being defined.
By default, the freedesktop.org.xml file is
installed to the packages directory in one of the
<MIME> paths (usually
/usr/share/mime/packages).
Table 5.1, “Child elements of <mime-info>” gives a brief
description for each of the elements that can occur as children to the
mime-type element.
Table 5.1. Child elements of <mime-info>
| Element (and attributes) |
Description |
| <glob
pattern="*.xyz"> |
This element specifies a glob pattern against filenames. If
the filename matches, then it is assigned the MIME type of the
parent mime-type element. The
pattern attribute is mandatory. |
| <magic
priority="50"> |
This element contains a list of match
elements as its children. The priority
attribute is optional, and specifies a priority between 0 and 100,
with 100 being the highest matching priority. Each child
match element has three required attributes:
type, offset, value and a fourth optional attribute,
mask. For details on these attributes, see the
XDG
shared mime info specification. |
| <alias
type="media/subtype"> |
This element defines an alias for the parent
mime-type element. An alias is simply a MIME
type that is sometimes known as another type. For example,
application/x-pdf is an alias for the MIME type
application/pdf. |
| <sub-class-of
type="media/subtype"> |
This element defines the parent
mime-type element as a subclass of the MIME
type specified in the type attribute. For
example, image/svg is a sub class of the MIME
type text/xml, text/plain,
and application/octet-stream. |
| <comment
xml:lang="locale"> |
This element provides a human readable description for the
MIME type. There can be zero or more occurrences of this element
as long as each one contains a unique value for the
xml:lang attribute. |
| <root-XML
namespaceURI="namespace"
localName=""> |
If a file is determined to an XML file, then this element
helps to further classify it through the use of the
namespaceURI and localName
attributes, both of which are required. The attribute
namespaceURI is the namespace of the document,
and localName is the name of the root element
for the document. If localName is present but
its value is empty, then the root element may have any name, but
the namespace must still match. |
The easiest way to understand these files is to take a look at an
example. Borrowing from the XDG shared mime
specification, Example 5.2, “Example of a source XML file:
diff.xml”
displays the contents of a source XML file called
diff.xml. This example defines the MIME type
text/x-diff. There are multiple
comment elements which give a human readable name to
the MIME type in a number of different languages. This MIME type has both
rules for matching through glob patterns and through
the use of content “sniffing” (better known as
magic rules). Any file with the extension
.diff or .patch will resolve to
this MIME type. Additionally any file whose contents start with the
strings specified in the value attributes of the
match element, will resolve to the
text/x-diff MIME type.
The order in which glob patterns and magic rules apply is beyond the
scope of this document. For details on this, see the XDG
shared mime info specification.
Example 5.2. Example of a source XML file:
diff.xml
<?xml version='1.0'?>
<mime-info xmlns='https://www.freedesktop.org/standards/shared-mime-info'>
<mime-type type="text/x-diff">
<comment>Differences between files</comment>
<comment xml:lang="af">verskille tussen lêers</comment>
<!-- more translated comment elements -->
<magic priority="50">
<match type="string" offset="0" value="diff\t"/>
<match type="string" offset="0" value="***\t"/>
<match type="string" offset="0" value="Common subdirectories: "/>
</magic>
<glob pattern="*.diff"/>
<glob pattern="*.patch"/>
</mime-type>
</mime-info>
