The attributes are specified within the starting tag of the element. Here the attributes are lib and sect . If the attribute value is one word, no quotes are necessary. The attribute name is typically limited to eight characters. In addition to tags, SGML also allow for the definition of entities.
Entities provide a means for simple keyword expansion.
This is useful not only for a shorthand notation, but also as a way of parameterizing a document to make future changes easy. Entity references begin with an ampersand and end with a semicolon. All entities are typically defined in the DTD . Entities are particularly useful to prevent text from being interpreted as markup. However, this should typically not be a problem because misinterpretation is only possible when these opening characters are followed directly by a non-space character.