Extra columns in discussion table like ForeignID and RegardingID
I'm implementing a LTI SSO plugin and I needed to create a Discussion programatically. I have done it successfully but, In order to detect the discussion when it has changed the name in the source plarform I need to store the source platform discussionId in the discussion table. The problem is that the discussionId in this table is autoincremental and, then, I cannot use this column for that. I have noticed that there are two columns that always contain null values and, by debugging I have seen they are not used. They are ForeignID and RegardingID. I have used the first one for my problem and is perfect but I'm afraid this column is used for a specific case. I have searched for information about this two columns but I haven't found anything. Can someone tell what is the purpose of this colums. Are they to use for cases like this or better not to use them because they are for another thing?
Thank you in advance.