The difference is as follows:
■ Outside link
・An external URL that starts from "http"
・The link title can be specified
*The link title does not change even if the link destination page name is changed.
■ Related manual
・A link to a manual from the same group
・The link title is determined automatically according to the title of the linked manual
*The link title cannot be specified.
・This link can be seen in "Referring manual" tab of other manuals "Usage status".
▼View data of individual manual (Web Browser)
https://teachme.jp/8/manuals/11837608