differnce from ansi sql standard - unicode strings?

Hello

I found BNF for SQL 2003 and I found there some small difference.
Standard use keyword ESCAPE, but PostgreSQL use keybord UESCAPE.

Anybody knows reason?
 <Unicode character string literal>    ::=        [ <introducer> <character set specification> ]        U <ampersand>
<quote>[ <Unicode representation> ... ] <quote>        [ { <separator> <quote> [ <Unicode representation> ... ] <quote>
}...]        [ ESCAPE <escape character> ]
 

thank you
Pavel Stehule