SkinInfo.xml is the only file required for any skin to be recognized by Messenger Plus!. The file needs to be placed in the skin's main directory. It is read when the skin is loaded or imported and contains several information related to the skin such as its name, its description, resources it replaces in Messenger, etc... its presence is also mandatory if the skin has to be exported into a Skin Pack.
Although this documentation has pages describing the most important elements of skininfo, many additional attributes and elements are supported for some features. These additional elements and attributes are only documented in the schema file. For that reason, you should always keep the schema's documentation on hand while reading on a particular subject to make sure you're not missing something that may help you understand or do something you thought was not possible.
The Schema file for SkinInfo can be temporarily placed in your skin's directory to validate your XML. The schema file must not be redistributed with your skin (it is useless in a public environment) so please remember not to include it in your Skin Pack. Here is how to write the first element of your XML file to make your XML editor aware of the schema file:
<SkinInfo xmlns="urn:msgplus:skins"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="urn:msgplus:skins PlusSkins.xsd">
<Information>
...
</Information>
</SkinInfo>
It is considered to be a good practice to always link your xml files to their respective schemas to prevent any possible run time error caused by a mistake in your XML. This header is not added in any example of this documentation for clarity reasons only. You should add it yourself every time you create a new skininfo file, without exception.
XML files tend to grow rapidly and you'll soon be thankful for the validation layer brought by the schema file. The modified SkinInfo element as specified above will allow your XML editor to confirm that your file is formatted correctly, with the proper elements and attributes, and that Messenger Plus! will be able to read it properly, thus removing a lot of common errors caused by misreading the documentation.
If your XML editor does not come with graphical browsing of the schema file, you can view a documentation generated by XMLSpy in the SkinInfo Schema Documentation section (some information may be missing in this documentation). Detailed information about each element can be found in the various other sections of this documentation. A view of the full diagram can also be found here.
SkinInfo Schema File, Schema Documentation, SkinInfo Diagram.