Names the image format for the bitmap that is provided with a <glyph-data> element. This element is used to define a private use character when the <private-char> contains a bitmap.
If a plain bitmap is included inline, the value of this attribute should be “PBM”, indicating that the plain text bitmap will be a human-readable matrix of zeros and ones.
|A word||A word naming the format of the bitmap. The word may not contain any spaces, and the characters of the word are limited to letters, numbers, and these special characters: period, hyphen, underscore, and colon.|
|Restriction: This attribute may be specified if the element is used.|