Is "to the extent where" grammatical? I know "to the extent that" is grammatical and on the list of dictionaries. But sometimes I come across sentences using "to the extent where" even in the newspapers though they are a few.
For the hybrid concept to gain wide acceptance, to the extent where Honda would benefit from being the market leader, Mr. Clarida said U.S. gasoline prices would have to reach $3 or $4 a gallon, at least twice the current level. (from nytimes)
1) I wonder whether "to the extent where" is grammatical or not.(even if informally it is used by some people)
2) "to the extent to which" is grammatical?
3) In "to the extent that", what can we call the "that" in terms of grammar?
conjunction which leads an appositive clause(like the "that" in "the fact that we are to blame)? or a kind of relatives?
Thanks in advance