Dear Scott McGee thank you very much for the tip, for some time I was looking for a solution to this animation.
But I forgot to mention something important the solid is linked to the text by the expression:
parent.sourceRectAtTime (). top -1098
So when I implement your suggestion does not work because the solid moves along with the text as in the example below:
https://giphy.com/gifs/6qq0BQAQBklFTPDMVC/html5
What I want from this animation is for the solid to align to the top of the text when typing any number of lines and then it is fixed so that I can animate position of the text as I did in the example below using keyframes and without any expression.
https://giphy.com/gifs/XJzx1kWwJkoddJXQKJ/html5
Thanks for all the effort and help!