In Apache, it’s possible to add a code to gzip/compress files, for example:

AddOutputFilterByType DEFLATE text/html text/plain text/xml text/css text/javascript

My question is, what is the difference between text/html and text/plain?

Is text/plain still necessary if you include text/html? I cannot think of any example where text/plain would be needed in an HTML document because text/html covers both HTML tags and “plain text” within them. Is my assumption correct?