What do `\<` and `\>` mean inside of a string?

    SubscriptBox["\<\"x\"\>", "\<\"y\"\>"] // DisplayForm

> $\text{x}_\text{y}$

The tutorials [String Representation of Boxes][1] and [Converting between Strings, Boxes and Expressions][1] don't seem to have any reference to this.


  [1]: https://reference.wolfram.com/language/tutorial/ConvertingBetweenStringsBoxesAndExpressions.html