php strtolower using?

Question

how can i use strtolower function?

Comments

What do you mean "how do I use?" Are you looking for the documentation? https://www.php.net/manual/en/function.strtolower.php

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i want to convert all words, text vb. to lowercase with php code not with css, i want to real convert. when i look into to database, it will be lowercase

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I wouldn't recommend doing that. Unless you have very compelling reasons to do so it's generally advisable to keep input data as-is and only (re-)format when displaying data.
With that said, from what I see you'd have to either patch core functions in qa-include/app/post-create.php (not recommended) or patch your editor plugin to lowercase text on submit in order to achieve the desired result.