Here is an example index.theme file:
[Icon Theme] Name=Birch Name[sv]=Björk Comment=Icon theme with a wooden look Comment[sv]=Träinspirerat ikontema Inherits=wood,default Directories=48x48/apps,48x48/mimetypes,32x32/apps,scalable/apps,scalable/mimetypes [scalable/apps] Size=48 Type=Scalable MinSize=1 MaxSize=256 Context=Applications [scalable/mimetypes] Size=48 Type=Scalable MinSize=1 MaxSize=256 Context=MimeTypes [32x32/apps] Size=32 Type=Fixed Context=Applications [48x48/apps] Size=48 Type=Fixed Context=Applications [48x48/mimetypes] Size=48 Type=Fixed Context=MimeTypes
The corresponding directory tree in the /usr/share/icons directory could look like this:
birch/index.theme birch/scalable/apps/mozilla.svg birch/scalable/mimetypes/mime_text_plain.svg birch/scalable/mimetypes/mime_text_plain.icon birch/48x48/apps/mozilla.png birch/32x32/apps/mozilla.png birch/48x48/mimetypes/mime_text_plain.png birch/48x48/mimetypes/mime_text_plain.icon
Where birch/scalable/mimetypes/mime_text_plain.icon contains:
[Icon Data] DisplayName=Mime text/plain EmbeddedTextRectangle=100,100,900,900 AttachPoints=200,200|800,200|500,500|200,800|800,800
And birch/48x48/mimetypes/mime_text_plain.icon contains:
[Icon Data] DisplayName=Mime text/plain EmbeddedTextRectangle=8,8,40,40 AttachPoints=20,20|40,40|50,10|10,50
In this example a lookup of "mozilla" would get the prerendered 48x48 and 32x32 icons before the SVG icons due to the order of Directories.