Making a letter bold in cursive scripts like Arabic script

Question

Consider Persian word سیب (/si:b/ apple). I want to make middle letter of it bold. Using the following code

س<b>ی</b>ب

produces

س ی ب.

How I can prevent the separation of the letters?

Answer 1

There is no predefined way for the browser/OS to connect Normal س to a Bold ی. It's somehow similar to have س and ی in different font sizes.

One workaround is to use Kashida before and after the letters:

ســیـب

Another workaround is to use Zero-width joiner:

س‍‍ی‍ب

Answer 2

As you describe, you do not want space between b tag, so you can use margin and padding set to 0.