One way to allow untrained input is to segregate the content from the formatting, so that plain text can be used as a source. This can be achieved using the PHP include command, with, or without, the HTML <PRE> tag. E.g.
<?php include 'file.txt' ?>
Will include the content of a text file called "file.txt" which is placed in the root directory of the site. The <PRE> tag causes the spaces and carriage returns to be presented instead of ignored.
Note: The PHP include function is a server-side command, and is not supported by the browsers. To use PHP commands, the source file must use the file suffix ".php" instead of ".html". PHP may not be supported by some free hosting accounts.