"oldsource" tag in QtLinguist

Adama W.

In the translation file of the project I contribute to, I notice a tag:

<oldsource></oldsource>

It is used as follows:

<message>
        <source>Display Properties</source>
        <oldsource>Display Node</oldsource>
        <translation>Afficher le Noeud</translation>
    </message>

Unfortunately, I don't know which sequence of actions led to lupdate generating that tag and I would like to know how so that I can use it to keep a record of previous states of a string. The only thing I was able to find through an online search was that it is the "previous content of a source (result of a merge)". I tried merging the local version of my file which had changes, to the version on GitHub but no "oldsource" tag generated. I would appreciate some help with that.
Thank you!

devjb

I also am interested in someone elaborating on that topic.

I already found out how to get rid of all obsolete strings by using -noobsolete as argument to lupdate.

However, those oldsource tags are something that I also not want to have. Is there a method to get rid of them other than hand edit the .ts file?