The same as when you're using plain text:

Example

1​1⁄2

Constituents

1. 1

2. Zero-Width Space:

   ​
   

   This is necessary to separate the superscript content of the fraction slash from the standard "1" without creating a gap.

3. 1

4. Fraction Slash:

    ⁄
   

   This converts its immediate neighbours to superscript and subscript versions.

5. 4

This is semantic.