Constant IMMUTABLE_PROPERTIES 

const IMMUTABLE_PROPERTIES: u64 = 0x0B;

Immutable Properties, Property Type 0xB.

Section 12.7: Immutable Properties are “a Track or Object Property that contains a sequence of Key-Value-Pairs (see Figure 2) that are themselves Track or Object Properties, respectively”. The Type is odd, so its value is length-prefixed bytes, and those bytes are another delta-typed run starting from 0.