The UL of each entry in the Essence Element Keys Register must begin with urn:smpte:ul:060e2b34.010201

Note that some Leaf ULs in the Essence Element Keys Register contain one or more Byte values 0x7f. These are “wildcards” that are substituted in implementations by a range of permissible values specified in a defining document. For example, SMPTE ST 381 specifies that Byte 14 of the Frame-wrapped MPEG Data Element is set to the number of Data Elements in the Data Item of a Content Package, and Byte 16 is an index to make each instance of this element type unique.