Sequence diagram markup needs some TLC

The UML sequence diagram from Markup feature is so close to being super super useful but some limitations make it very frustrating to work with.  They are things I am thinking can be easily fixed.

• If a swimlane name is too long it does not auto-resize the box with the name it leaves it blank.  I have to manually resize the whole sequence diagram.  And then when I press Build again it goes back to the original size and I have to resize all over again
• The alt markup syntax is really unwieldy and very easy to get wrong; it's a pain it all has to be on one line.  Also as far as I can tell the alt markup only allows one step per alternative case.  I'm just using 'opt' instead.
• When I have a long line in the markup (like for an alt sequence) I can resize the pane but when there is an error on Build the UI gets very confused and I can only see half of the text and I can't scroll back to the left to see the rest of it
• If I don't do a successful Build then my markup gets completely lost - there is no auto-save
• It should update the UI every time I finish a line rather than make me push a Build button
• I'd like to color code swimlanes without ungrouping and losing the markup
• I should be able to generate markup from any grouped sequence diagram as long as it follows certain rules