Enlightenment DR17 use freedesktop.org .desktop files according to the
XDG Desktop Entry Specification version 0.9.4, icon themes according to
the XDG Icon Theme Specification version 0.11, and menus according to
the Desktop Menu Specification version 0.92.  There are some extensions
though.


.desktop extensions.

Two extension fields are defined as allowed by the specification. 

X-Enlightenment-IconPath is used to specify an absolute or relative path to
an icon file.  If it exists it overrides any other icon specifications.

X-Enlightenment-IconClass is used to specify a list of icon classes. 
This is the same information that was in .eaps as app/icon/class, and is
used the same way if it exists.  Obviously any .desktop file that comes
with packages outside of E is unlikely to have that field.  One further
twist is that if the icon classes are not found in edje, then icon class
becomes a list of icons to search in the standard FDO way.

The standard Icon field is also treated differently.  If it contains a /
it is considered to be an absolute path, or a path relative to the
location of the .desktop file.  Otherwise, if no icon class was
specified in the .desktop file, then the Icon, Exec, and Categories
fields are used in that order to build an icon class.  Everything but
the Icon field is lower cased.

This means that for standard .desktop files, with out the extension
fields, icons in the E theme are searched for first, then icons are
searched for in the usual FDO way, unless the Icon field specifies a
path, then it is simply used with no searching.  Converted .eaps should
just copy the app/icon/class data to the X-Enlightenment-IconClass
field.


Icon theme extensions.

.edj files are searched for before the other types of icon file.  The
"icon" group is used to specify the graphics for the icon.  It is up to
the code using the result to allow full edje interactions and
animations, and people that write that code are encouraged to support it
all.