How do I make sure 'text' fills the entire figure?

I'm writing Matlab code that other people will run on different OS, Matlab versions, screen resolutions, etc. Part of the code makes a figure with text only (it sounds silly, but it's useful). I want to make sure the text fills the entire figure, e.g. doesn't overflow the figure, starts at the left bound and ends at the right bound. How do I do this?

I tried using text's 'Extent' property, but this doesn't work since text characters remain the same size whatever the axes.

[Walter Roberson]

? Text characters do not remain the same size in all screen resolutions. Not unless you are using MS Windows or OS-X (not Linux) and you specify the positions in "characters", in which case it becomes pretty much the same as if you had specified the positions in "points" (points are 1/72 of an inch.)

Is the idea that the text font size is to be scaled, or is the idea that more text or less is to be put up to fill the available space?