extend "Header Compression"

Author: soc

_runtimes/header-compression.md

@@ -60,6 +60,12 @@ Schemes to decrease header size often trade in a more compressed representation
      64 byte granularity, 1 GiB address space (type 7)¹   8 byte granularity, 512 GiB address space (type 4)²
 </div>
 
+Examples for "other uses":
+- marked bit
+- pinned bit
+- locked bit
+- forwarding (failed) bit
+
 ---
 ¹: [Pointer Compression Type 7](pointer-compression#type-7-vtabletypeclass-reference-64-byte-granularity-1-gib-address-space)<br/>
 ²: [Pointer Compression Type 4](pointer-compression#type-4-normal-reference-8-byte-granularity-512-gib-address-space)