[If Expressions][Then]do this[/Then][Else]otherwise this[/Else][/If]
To display some HTML (or execute WebDNA [xxx] tags) only if certain conditions are met, place the text inside an [If] context. The comparison, which may contain any [xxx] tags, is first evaluated to see if it is true, and if true then the contained [Then] context is executed (or simply displayed, if it's just HTML). If not true, then the contained [Else] context is executed (or simply displayed, if it's just HTML). See [Then] and [Else].
Example (normally you would put the following text into a .tpl file on your server and use a web browser to link to it):
[If (("[username]"="Grant") | ([grandTotal]<100)) & ({[date]}<{2/15/2000})]
[Then]either username was Grant or grandTotal was < $100 and it's not Feb 15, 2000 yet[/Then]
[Else]The complex expression wasn't true[/Else]
[/If]
See [If] for description of full syntax.