If a line begins with a semicolon (;), it is considered a comment.

Example:

Windows Registry Editor Version 5.00

; These are Command Processor Values
\[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Command Processor\]
"AutoRun"=""
"CompletionChar"=dword:00000040
"DefaultColor"=dword:00000000
"EnableExtensions"=dword:00000001
"PathCompletionChar"=dword:00000040