For html strings you have to replace the special characters with the entity names (e.g. replace

'<' by '&lt;' or 
'>' by '&gt;'

).
For a description to entity names and a list of the important ones see https://www.w3schools.com/html/html_entities.asp
A full list character entity names can be seen in https://dev.w3.org/html5/html-author/charref.

@darsh – yes it is possible using <div> or <tr>/<td>, but this has some drawbacks:

hButton.String = 'Left-aligned'

Instead, I suggest using the text alignment methods/properties of the underlying Java control: http://undocumentedmatlab.com/blog/button-customization

@Meade – it’s not Matlab that ignores the align directive but rather the underlying Java Swing behavior, which snugly fits the text in the center of the button, and of course aligning text within a tight-fitting box has no effect. The workaround I suggested simply forces Swing to use a non-tightly-fitting boundary box, within which you can indeed align the text. It’s a pretty standard HTML/CSS behavior workaround, and any decent web developer could probably find several similar alternatives.

@Yair

This is a great work-around!
I’m guessing by your suggestion that Matlab doesn’t interpret any of the ‘align’ commands for text in naked Matlab uibuttons?
As for suggestion two, I’m very familiar with your great |findjobj| utility. I use it all the time. I was hoping to avoid jButtons if possible, but they might be best choice afterall.
Many thanks!
meade

@Meade – You can use an HTML string such as this:

pxPos = getpixelposition(hButton);
hButton.String = ['
text'];  % button margins use 20px

A better solution is to use the findjobj utility as explained here. This would be independent of the button’s pixel-size and would work even when the button is resized.

hButton.String = '
My RIGHT ALIGNED string';

Much thanks for all you do!