Question about developing a new XFCE app

[Apostolos Chalis]

Hello everybody, my name is Apostolos and I use XFCE and KDE. Around 
every six months I switch between the two and every time that I switch 
from KDE to XFCE I miss Okular (yes I am aware that I can use it on XFCE 
too but it does not feel the same due to the differences of Qt and GTK). 
I am running a university student chapter of ACM that has some capable 
young developers in it and I am thinking of proposing to them to write a 
GTK PDF viewer. I am sending this mail to ask you what is the official 
way of making a XFCE official app just like Thunar. Thank you in advance.

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Kind regards
Apostolos Chalis | Scientific associate of member of AUTh