A comment is a piece of text in your xCss file that you do not want to appear in the final output.

Basic CSS, already supports C-style block comments, of the form /* a comment */. These work fine but are unwieldy, as you must have both opening and closing braces.

xCss adds support for C++ / C# / Java-style line comments, which comment from the marker to the end of that commented line.

This makes it easier to use comments for;

Full-line notes
(or multi-line notes), which only the developer needs to see. These are often used at the top of a CSS file to for file-specific developer notes, or are used immediately preceding a section of CSS code, to comment on various implementation details.
// This is a note regarding the following section
// of CSS code...
Code deprecation
to temporarily or permanently remove a line of CSS code which is not currently wanted, but should remain for documentation purposes.
li {
	background-color: green;
//	color: #f00;
	font-size: 20pt;
In-line comments
Add notes to the end of code lines to clarify your source code.

Inline comments treat everything after the comment marker (//) until the end of the line as a source-code comment, and this text is not emitted in the final output. Everything before the marker is preserved untouched.

color: #f00; // red