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extract() checks for colissions with existing variables. the way collisions are treated is determined by extract_type. it can be one of the following values:
it also checks for collisions with existing variables in the symbol table.

by contrast to strtolower(), 'alphabetic' is determined by the unicode character properties. thus the behaviour of this function is not affected by locale settings and it can convert any characters that have 'alphabetic' property, such as a-umlaut (Ä).
see also strtolower(), mb_strtoupper(), mb_convert_case().