Most characters in an XML document can be expressed as regular Unicode codes. Characters not in the standard Unicode tables have traditionally been expressed as explicit font calls (non-portable), created as inline graphics, or defined in one of the Unicode Private Use Areas where users may define their own characters. This element is used when there is known to be no font available to render a private-use character. The <glyph-data> element provides information on the actual glyph that is associated with the private-use character.
The DTD Suite has been designed with Unicode as the basic representation of all special characters. The use of combining characters is supported and encouraged, as is the use of entities defined by the STIX project (http://www.ams.org/STIX/). Unicode values in planes other than Plane 0 may be freely used. Use of private publisher entities and Unicode Private Use Area is discouraged but supported with the <private-char> element, for which a corresponding bitmap must be submitted using the <glyph-data> element. In cases where an entity name has been generally accepted with a corresponding Unicode number and the entity has not been added to the ISO standard entity sets, a named entity may be defined in the %chars.ent; module (e.g., as has been done for the Euro €).
Because of the potential for conflicts in assignments by different publishers, this DTD Suite does not support assignment of values in the Unicode Private Use Area. Publishers who have defined characters in the Private Use Area must remap those characters to existing Unicode values (using combining characters for special accented characters where appropriate) or must submit bitmaps of those characters using one of the two methods supported under the <private-char> element. Those custom publisher entities for which corresponding Unicode values have not been determined must be tagged with the <private-char> element.
The element <glyph-data> includes an inline bitmap of the glyph encoded in PBM (Plain Bit Map) format so that it is human-readable. (See the tagged example below.)
<!ELEMENT glyph-data (#PCDATA) >
Text, numbers, or special characters
... <p>... The map symbol indicating these conditions will be a <private-char name="NORTHWEST SOUTHEAST ARROW" description="Arrow, normal weight, single line, two-headed, Northwest to Southeast"> <glyph-data id="NWSEArr" format="PBM" resolution="300" x-size="34" y-size="34"> 0000000000000000000000000000000000 0111111111111100000000000000000000 0111111111111100000000000000000000 0111110000000000000000000000000000 0111110000000000000000000000000000 0111111000000000000000000000000000 0110111100000000000000000000000000 0110011110000000000000000000000000 0110001111000000000000000000000000 0110000111100000000000000000000000 0110000011110000000000000000000000 0110000001111000000000000000000000 0110000000111100000000000000000000 0110000000011110000000000000000000 0110000000001111000000000000000000 0110000000000111100000000000000000 0110000000000011110000000000000000 0000000000000001111000000000000000 0000000000000000111100000000000110 0000000000000000011110000000000110 0000000000000000001111000000000110 0000000000000000000111100000000110 0000000000000000000011110000000110 0000000000000000000001111000000110 0000000000000000000000111100000110 0000000000000000000000011110000110 0000000000000000000000001111000110 0000000000000000000000000111100110 0000000000000000000000000011110110 0000000000000000000000000001111110 0000000000000000000000000001111110 0000000000000000011111111111111110 0000000000000000011111111111111110 0000000000000000000000000000000000 </glyph-data></private-char>. The NOAA 1993 standard definition of <private-char name="NORTHWEST SOUTHEAST ARROW" description="Arrow, normal weight, single line, two-headed, Northwest to Southeast"> <glyph-ref glyph-data="NWSEArr"/></private-char> will apply. </p> ...