HotDog uses several syntax files to validate any HTML you create. These syntax files are separated by HTML versions and browser support. For example, if you want to use only tags that are HTML version 3.2 compliant, you can specify that only allow HTML 3.2 tags are considered valid. This means that any tags or attributes that don't form part of this specification will be underlined.
In the Edit menu, choose Preferences and then navigate to Syntax Filters.
Using the Language drop-down list select HTML.
Using the Filter Rule drop-down list select the syntax specification you wish to use.
Click OK.