how to use comment in html code example

Example 1: commenting in html

<!-- a comment in html -->

Example 2: html comment

<!--This is a comment in html.-->
<!--You can put comments enywhere! It does not care if it is mid peice of
code in a peice of code! You must put the ending arrows in or it will
think everything is a comment! Note you can comment over multiple lines.
Use a ! at the start arrow, this may not make sence as the rest of
html uses tags where ! is at the ends.-->

Example 3: html note

<!-- This is an HTML note -->

Example 4: comments html.erb

#You need mix html comments tag and ruby comments tag : 
'#' and '<!-- -->'