[whatwg] HTML parsing: "act as if...had been seen" using what insertion mode?

[David Flanagan]

The HTML parsing algorithm frequently includes directions like "act as 
if an end tag with the tag name 'p' had been seen".

Suppose the insertion mode is "in caption" mode.  It tells me to process 
a token using the rules for "in body" mode.  Then, while processing a 
token using those rules, I need to act as if a </p> tag or </option> tag 
had been seen.  My question: what insertion mode do I use to process 
that synthetic end tag?

Perhaps the spec could be modified to add a definition for "act as if" 
along with the definition for "using the rules for".

     David