Grail's support for iconic entities is both extensible and customization. This discussion covers both issues, as the mechanism is the same.
For each iconic entity supported by Grail, a small GIF image is
provided in the distribution. These images are located in the
icons/ subdirectory of the Grail source directory.
Entities are loaded on demand from this directory if no alternate
image has been provided.
Within each user's GRAILDIR, the directory
icons/ is used to provide alternate images for each icon.
Each alternate must be a GIF image file containing the image to be
used. The images may be any valid single-image GIF file; transparency
is fully supported as with all images used in Grail. For entitity
ref, the file
GRAILDIR/ref.gif is used as the image source
if the file is available. If the file is not provided, the image
supplied with Grail is used.
A user can change the appearance of the icon associated with an
image by creating a new icon and placing the GIF file in their
GRAILDIR/icons/ directory. The icon can be any size,
though we recommend that the icon be approximately as high as the
normal text font and that the number of colors be fairly limited.
The entity set can be extended by each user by adding additional
image files to the GRAILDIR/icons/ directory. Extending
the set for an entire site can be done by adding new images to the
icons/ directory of the Grail source distribution.
SGML general entity references, including those used in HTML, are case sensitive. For platforms with case-sensitive file systems, this should be considered when adding new images.