The EntityAddEntity function adds an entity definition to an entity codec control structure.

The argument ptr points to the control structure. The text that defines the entity is stored in the structure pointed to by the argument entity.

An entity is often used as short hand for repeated text, to refer to symbols that would otherwise confuse the XML passer, such as "<" or ">", or to refer to external data.The entity codec encodes and decodes entity/symbol pairs.