Use Hector the Inspector guy. You can access it by clicking on “guy in a hat” icon in Status Bar or via Code | Configure Current File Analysis... from the main menu.
Once there you can move the “Highlighting Level” slider from “Inspections” to “Syntax” .. or even “None” in case of a large or complex file.
Notes:
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Settings here affect current file only (excludes “Power Save Mode” option)
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Depending on a file, you may have multiple sliders (e.g. in
.phpfile you will see separate sliders for HTML and PHP languages: this may change depending on some other settings):
P.S.
If your file is actually part of the library (PHP or JavaScript; “Library” in terms of IDE, of course) then they by default should not have inspections enabled in them:
UPDATE 2021-06-11:
Hector the Inspector has been removed from the status bar since 2020.2 version or so. You can get it back by installing Hector the Inspector plugin from Settings/Preferences | Plugins