Why do all PHP parse errors start with "T_"?

Question

I just want to know is whether there is any reason/story behind to use T_ before parse errors like

parse error : unexpected `T_`ELSE in ... blah blah blah  
parse error : Unexpected `T_`IF in ....blah   
parse error : unexpected `T_`VAR  
parse error : unexpected `T_`STRING

and many more.

Can you provide any link for clarification? Also, are there any other prefixes used in error displaying then please share.

Answer 1

T stands for Token.

These errors are telling you that the parser found a token that it didn't expect.

Answer 2

Because those are, from the point of view of a parser, tokens, thus the T_ (that's the same reasoning why error levels start with E_ ...).