In Freeway you could select the item in the site panel and hit return or enter to drop into that box. from there you could select the text. We don't have that in Xway
1. Select the item in the Site panel
2. Press Tab to switch out of the Site panel
3. Press Command-Return to edit text within the box
Rather than adding the positioning style as an extended item I tried changing the position property using the inspector. Unfortunately every time I changed the item from relative to absolute it would add a top:0 and left:0 style which prevented the vertical alignment code from working. If I stripped these values out they would come back each time I switched the positioning back again.
You don't need to keep changing the position property, but the reason that Xway adds top and left offsets is because this allows you to drag the box after you've converted it.