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White space is not permitted between the markup declaration open delimiter(“<!”) and the comment open delimiter (“--“), but is permitted between the comment close delimiter (“--“) and the markup declaration close delimiter (“<”). A common error is to include a string of hyphens (“---“) within a comment. Authors should avoid putting two or more adjacent hyphens inside comments.
Information that appears between comments has no special meaning (e.g., character references are not interpreted as such).