2.2.4.13 byte_count

These extensions allow a higher-level protocol to specify the memory size in bytes of a given parameter as the value of another parameter. This MUST be specified by the byte_count parameter<52> attribute in an ACF, which the implementation MUST interpret as calling this extension.

 [function-attribute-list ] function-name(
     [byte_count(length-variable-name)] parameter-name,
     ...);