The usual purpose of this tag is to create a PNG or GIF image containing
a background image and to expand to its filename. Its contents is
specified via the content attribute by use of size/color pairs.
Usually the created images are named
imgbg-xxxxxx.png where xxxxxx is the content id of the image.
When you use a
base=foo attribute, then the resulting files are named
foo.imgbg-xxxxxx.png. Actually you can even use a complete filename
including a directory prefix, i.e. when you use base=../../common/foo
attribute, then the images are created as
../../common/foo.imgbg-xxxxxx.png.
And for most flexibility when no base is specified and the variable
BGIMG_BASE is defined (usually from within a .wmlrc file via
-DBGIMG_BASE~path/to/imgbg/dir/base) it is used. Use this feature to
redirect the created images to a particular directory.
You may also use the variable IMAGE_BASE which defines in a single line
all base names for images generated by WML.
By default, GIF images are generated. This attribute lets you use an
alternate image format (actually only PNG and GIF are recognized).
You may also change the default format with the variable IMAGE_FORMAT.
This is a comma-separated list of size/color specifications
``pixels:#rrggbb:#rrggbb:slices''
The last two arguments are optional, only present for gradient images.
In this case, a linear gradient line is drawn from color 1 to color 2,
with slices different colors.
To get a background with two columns, a black one with 150 point in size
and a white one which fills the rest of the page use
``150:#000000,1200:#ffffff''.
