I read from several books and grammar websites that we don't use "would/will/shall" in "If clause".
But I was looking up the meaning of a word in Cambridge dictionary and I got stunned to see there "would" used even in "If clause".
The sentence is here:
"If you would move sideways to the left, I can get everyone in the picture."
In the above sentence the modal future "would" has been used in the "If clause" either.
I'd like to know: why is the word "would" used in that if-clause, although the grammar books say not to do so.