[M4IF Technotes] Descriptor Length Field

[Trevor]

Dear Experts,
According to "ISO/IEC 14496-1:2001", the syntax of any descriptor does 
NOT contain a length field. But in the annex J (Graphical representation 
of osbject descriptor and sync layer syntax), there is a length field 
right after TAG field. Could anyone here tell me what this length field 
represents and how it is encoded?
Thanks in advance,
Trevor