This document discusses the format of Theme (.theme) files used in Windows 7 and Microsoft Windows XP. A .theme file is a .ini text file that is divided into sections, which specify visual elements that appear on a Windows desktop. Section names are wrapped in brackets ([]) in the .ini file.
Windows 7 supports new features including the Desktop Background Slideshow. Unrecognized sections of a .theme files are ignored by previous versions of the operating system. A new file format, .themepack, has also been introduced with Windows 7 to help users share themes.
Theme files have a number of required and optional sections. The document from Microsoft, describes the sections of .theme files and provide examples of how to specify changes for the different elements like themes, image, colors, sound, slide show, metrics, visual styles, etc.
A very useful must-read for themers !
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MSDN.