Auto merge of #27556 - taliesinb:tarpl-clarity-2, r=Gankro
Auto merge of #27556 - taliesinb:tarpl-clarity-2, r=Gankro

* Some clarifying rephrasing.
* Rename B.x back to B.a.
* Make null pointer optimization section bit more concrete.

r? @Gankro 

GBGamer/rust,aidancully/rust,l0kod/rust,graydon/rust,l0kod/rust,dwillmer/rust,aidancully/rust,pshc/rust,l0kod/rust,aidancully/rust,graydon/rust,zubron/rust,dwillmer/rust,GBGamer/rust,dwillmer/rust,pshc/rust,zubron/rust,pshc/rust,GBGamer/rust,zubron/rust,zubron/rust,dwillmer/rust,graydon/rust,zubron/rust,GBGamer/rust,aidancully/rust,dwillmer/rust,zubron/rust,dwillmer/rust,pshc/rust,GBGamer/rust,GBGamer/rust,l0kod/rust,l0kod/rust,graydon/rust,l0kod/rust,l0kod/rust,GBGamer/rust,graydon/rust,pshc/rust,zubron/rust,aidancully/rust,pshc/rust,zubron/rust,GBGamer/rust,dwillmer/rust,aidancully/rust,dwillmer/rust,pshc/rust,graydon/rust,pshc/rust,l0kod/rust