Highlight invalid keywords

Change-Id: I94ab1e668b8dd5a09c6c80efe0a16465d0744df7
Highlight URLs

Change-Id: I19b8e37c1775165c20af6636673f02369816b30d
Only highlight FIXME/TODO/XXX in comments

Change-Id: I2f9e75ce045a7bf7e81659ead8d69a60f265e85d
Always make a back trace during circular evaluation

Change-Id: I2f92f15d47c730e7fd2f436bcf0d045d7ef780b3