__FILE__ shows what file you are working with and __DIR__ shows what directory you are working in.
is_readable();check to see if the file is readable and if it exists.
feof(); check to see if the pointer is at the end of the file.
fopen($filename, 'w'); opens file for write, truncates the file.
fopen($filename, 'a'); opens file for write, appends to the current file.
fopen($filename, 'c'); opens file for write, appends to the beginning of the file.
<br>- line break in HTML
<img> - image
<input> - form input
<meta> - metadata tag
add an id="...." into the < > in order to assign an attribute to a tag. Make sure to prevent spacing between id = and "...".