If you are moving from point A to point B and you pause in the middle - You actually did not reach the end of your tween. If you press start again you will continue previous motion until you reach the end. In this case "Start tween" works like a "Resume current tween".
While stopping the tween will mark your current position as the end position. Pressing Start should not do anything until you set new target.
Don't know... maybe I'm overthinking this.
And one more expression could be useful - "Current time". To return how many time, in seconds have passed from start of the tween. For example if your tween duration is set to 7 seconds. It will return value between 0 (start of the tween) and 7 (end of tween)
This could be a nice addition to stack things up. Or do something else at very specific time of the tween.
Sorry for all this requests (moaning about) but this plugin is so nice and so simple to use. I've been using it for last few days and it saves me already a lot of time.
No need to apologize. It's good to have feedback and I'm glad you're already finding it useful.
On both of these points, it's starting to get outside of how I intended the tweens to work. However, I think you could approximate both by using existing functionality. For your "stop" action, you could pause the tween and then re-configure it to the new values. For the "current time", you could chain multiple tweens with the on end conditions. (I might consider mid-tween conditions at some point, but it would be a bit complicated to implement.)
One note of caution on making use of Twixt in its "in progress" state: things could break at any time! (Or, indeed, already be broken.) I don't recommend it yet for production use. But if you do, be sure to back up before you install a new version! Hopefully I'll have it hammered out enough for a 1.0 release in a few weeks.