Are you sure you looked in Designer 6 Help? It is not in earlier releases. It is only in Designer 6.
Anyway, here is a demo. This code in a button in my journal database creates a new document containing a URL link. The indentation is only to make it easier to read here in the forum, of course:
Sub Click(Source As Button)
link$ = "LDD"
url$ = "http://www.notes.net"
Dim session As New NotesSession
Dim db As NotesDatabase
Set db = session.CurrentDatabase
Dim stream As NotesStream
Set stream = session.CreateStream
stream.WriteText {<?xml version='1.0' encoding='utf-8' ?>
<database xmlns='http://www.lotus.com/dxl' version='6.0'>
<document form='JournalEntry'>
<item name='Subject'><text>DXL demo</text></item>
<item name='Body'>
<richtext>
<par>
<run>Click on this link: </run>
<urllink showborder='false' href='} & url$ & {'>
<run><font color='system'/>} & link$ & {</run>
</urllink>
</par>
</richtext>
</item>
</document>
</database>}
Dim dmp As NotesDXLImporter
Set dmp = session.CreateDXLIMporter(stream, db)
dmp.Process
End Sub