SNOMED CT Expression Constraints may also include comments inline within the constraint string to explain, describe or document different aspects of the expression constraints. Each comment begins with a forward slash directly followed by a star (i.e. "/*") and ends with a star directly followed by a forward slash (i.e. "*/"). Comments may be placed anywhere in an expression constraint where whitespace (i.e. "ws") or mandatory whitespace (i.e. "mws") is allowed.

Comments have no effect on the machine processable interpretation of an expression constraint, as they should be ignored during evaluation. For example, the following two expression constraints (the first with comments, and the second without), will evaluate to exactly the same set of concepts:

   /*  Disorders of lung with edema  */
19829001 |Disorder of lung| /*  Descendants of disorder of lung  */
116676008 |Associated morphology|  = <<  79654002 |Edema|
         /*  Where the associated morphology is edema or a subtype  */

A comment may include both stars and forward slashes. However a star may never be directly followed by a forward slash within the middle of a comment, as this combination denotes the end of the comment.