"If search is an array and replace is a string, then this replacement string is used for every value of search. The converse would not make sense, though. "
I think one important (and not at all vaguely theoretical) use-case is completely ignored here. Take, for example, the way the PDO handles parameter replacement.
If we have the following query:
"SELECT * FROM my_table WHERE (id = ? AND my_column = ? AND other_column = ?);"
The "?"s should be replaced by each successive variable in a $parameters array. That is EXACTLY the use case for "search" being a value and "replace" being an array.
Considering that this is not only a real-world example but also part of a core PHP functionality I find it very strange that it's dismissed so easily here.
