I don't know that a URL is exactly what it is that I am pasting. In the Forum case, I highlight and copy the title. When I paste that into TextEdit, email, or KBM Comments, it comes in as the title text with a hotlink to the hidden URL.
I have been presuming that what's literally on the clipboard is HTML or RTF or some other "standard" link format that is then interpreted by the pasting app into its own format.
I found out more information about the format of links on the clipboard from JMichaelTX and @ccstone in:
How to Use RegEx to Extract URL and Link Text from HTML Anchor Code?
from 2015.