For creating skins I'm using Serna Free xml editor. It's obsolete, it's code is open sourced on GitHub, and I couldn't make anything without it. It's WYSIWYG, so you don't deal with any notepad-like coding. You can move elements (PVD fields and other elements) through the tree and in PVD to refresh the skin to immediately check results.
Serna Free is 12 years obsolete, but still working properly, but it's not easy to find it today, so you probably have to use some torrent downloader if you want to find, download and use it. I didn't find any other xml editor that is near Serna, just like there is no movie database program near like PVD.
Once you try it, you will never use anything else for at least skinning PVD.