Sending Custom `header()` Responses from Evolution CMS Export Logic

If a download script must emit its own headers, the main task is to make sure nothing in the CMS boot process has already sent conflicting output.

The original example used a custom export flow with headers like:

header("Expires: Mon, 1 Apr 1974 05:00:00 GMT");
header("Last-Modified: " . gmdate("D,d M YH:i:s") . " GMT");
header("Cache-Control: no-cache, must-revalidate");
header("Pragma: no-cache");
header("Content-type: application/vnd.ms-excel");
header("Content-Disposition: attachment; filename=exim.xls");

and the key question was why MODX/Evolution was not sending them cleanly.

What Usually Breaks Header Output

whitespace or HTML output sent too early
bootstrapped CMS rendering continuing after the export logic
plugins or templates injecting output before the download starts

The practical pattern is to isolate export logic in a clean execution path, send headers first, emit only the file content, and stop the normal page render immediately after.

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