Where a link starts and ends
A link starts at http://, https://, ftp://, ftps:// or www. and runs until the first space, quote mark (straight or curly) or angle bracket. A long dash, an ellipsis, a closing guillemet and the full stops, commas and brackets used in Chinese and Japanese also end it, because those texts have no spaces. That is how a link inside HTML (href="https://example.com/a") or Markdown ([text](https://example.com/a)) is read correctly.
Punctuation at the very end belongs to the sentence, not the link. In Read https://example.com/help. the link is https://example.com/help. Brackets are matched: https://en.wikipedia.org/wiki/Rust_(language) keeps its closing bracket, while a bracket that closes a sentence outside the link is dropped.
What is not treated as a link
A bare domain such as example.com/page has no marker that tells it apart from a file name or a number with a dot in it, so it is not included. Add https:// or www. in front if you want it found. Email addresses are also not links, and mailto: and tel: are left out. Use the email extractor for addresses.
A link that contains a space, a quote mark or an angle bracket ends at that character, because those cannot be written as they are inside a link.
Seeing which sites are linked
Site name only reduces each link to its host in lower case, so https://Docs.Example.com/a?x=1 becomes docs.example.com. The summary under the result counts links per site across all matches, before duplicates are removed. It is a quick way to audit where the links in an article, a report or a page of search results go.
Links are compared exactly by default, including upper and lower case, because the path of a link can be case sensitive on many servers. Turn on Ignore case to merge them.