[angeliszotis]

Fixes #2680

The first note in the Notes section of the header() page reads:

You can use output buffering to get around this problem, with the overhead of all of your output to the browser being buffered in the server until you send it.

There is no problem mentioned before it. The note that comes right before is the SAPI one, which comes from the note.network.header.sapi entity:

Headers will only be accessible and output when a SAPI that supports them is in use.

so a reader going through the Notes section has nothing to attach "this problem" to. What it refers to is in the Description section:

Remember that header() must be called before any actual output is sent, either by normal HTML tags, blank lines in a file, or from PHP.

As the reporter pointed out, that is also not really a "problem" by itself. It is a requirement, and it only becomes a problem if something is output by accident.

I rewrote the opening clause so the note stands on its own:

Output buffering can be used to avoid the requirement that nothing is output before header() is called, with the overhead of all of your output to the browser being buffered in the server until you send it.

The rest of the note, the part about ob_start(), ob_end_flush() and output_buffering, is unchanged.

[lacatoire]

Thanks @angeliszotis, few linter nits, but LGTM

[angeliszotis]

Thanks @lacatoire! Switched the note to simpara to clear the style check.