Nameloc for non-SGML entities
Locates one or more entities containing non-SGML data (e.g. the graphics, a video clip, etc). If it locates several entities they must contain identical or alternative information, e.g. a figure that exists in several storage formats that may be substituted for each other depending on system capabilities.
For further explanations, see the HyTime standard (ISO 10744), clause 8.3.2.1.