Sometimes, especially ’some’ mobile browsers do not respect the cache-headers you set in html meta tags or as htm headers with php. This is particularly annoiying, when your page or webapp has an error, like a typo or something, that does not get fixed on the client side unless they purge their browser caches manually (and why would they do that?) And in the case of a webapp, they cannot even do that.
So the only secure way is to always load the whole page from another file, adding a changing parameter to the URL so it really is different I have found this working nicely even in webapps installed on the user’s device. They pull the content nicely from a remote fileeverytime they open.