built-in entity
external-text-entity #capacity OR (when | unless) entity is #capacity
A type of attribute of an external text entity that defines the capacity set (storage limits) in an SGML declaration.
A capacity set can be either specified in the SGML declaration or described by a public identifier. If a public identifier is provided then its text must be a sequence of zero or more capacity names, each followed by a capacity points number.
Each name in an external capacity specification must be that of a capacity. The associated number becomes the limit value of that capacity. Any capacity not mentioned is set to the reference value (35000). An external capacity set description can contain either no text, or only comments and white space. In either case, all the capacities are set to the reference value.