Doubt on "holder"-related strings

Sorry if this is not the proper place. If I should ask this somewhere else, please let me know.

While translating Calls, I found two strings which are not very clear to me: Call holder and The holder for this call, both from the bottom of src/calls-call-selector-item.c. I built and installed calls in my Arch Linux, but wasn't able to find this string (tried calls -p dummy). They seem to be a label and tooltip, but not sure.

Can some please clarify to me how these strings are used?