A colon is used after each Lasso tag to seperate the tag name from the tag parameters. If a tag does not have any parameters then the colon is optional.

[TagName: Tag Parameters]

<?LassoScript
  TagName: Tag Parameters;
?>

In previous versions of Lasso either a colon or a comma could be used after a tag name in all tags. In LDML 5 only a colon is allowed. Use of a comma is now a syntax error.