The Flex SDK page has a spec titled “ASDoc in MXML“.
Currently there is no way for users to add documentation to components defined in mxml files. The asdoc tool doesn’t read the comments in mxml files. Increasingly more components in the flex framework are being written in mxml.
Adding support for mxml in the asdoc tool would help developers to generate documentation for their components.
Several customer have also added requests in JIRA to support class level comments in mxml files.
So now you can add ASDoc comments by the syntax <!— asdoc comment –> . The — are necessary for the compiler to understand that they are ASDoc comments.
To get the full details chect out the spec : ASDoc in MXML.