What is enable markup in text in 2D screen?

is there any demo available for the same?

Looks like some of the recent work done to element text to add use colours in a substring of the text.

My guess is that they will extend it to do more such as add styles to substrings.

Changing the color of a text is working after enabling the markup, But how to add substring for the text

Currently not supported at the moment.

Just in case someone is stumbling on this, as I did:
The unicode font range for the numbers as subscript is U+2080 to U+2089. You can add these as a custom range in the font asset settings. These numbers are hex already so it would be from 0x2080 to 0x2089 for subscript numbers. This is not a real alternative for layouting text etc, although there is a wide range of superscript und subscript characters, but if you just need to display chemical formulars like me, it is sufficient.