Created attachment 6085 Patch tooltip and secondary icon As we have discussed in the mailing list and $xfce-dev, we notice that the ability to use custom formats with pango markup seems like a hidden option for some users. Besides the current tooltip in the custom text entry, we need something more compelling, to let the user know about this and "lure" him to http://docs.xfce.org/xfce/xfce4-panel/clock#label_and_tooltip_markup. The attached patch uses a secondary icon and a tooltip. Maybe a popover(GTK3) instead of the tooltip, with a label(same text of tooltip) and button that opens the docs.
Created attachment 6086 Patch new preset Another suggestion is to create add a new preset that uses pango markup.
Not sure I understand the first patch, the tooltip already says "See the "Help" page for additional information." I guess we can make it say "See the "Help" page for additional information and further examples." I tried your patch and it may be Gtk+3 playing tricks on me or whatnot, but I don't see a secondary icon in the tooltip and nothing seems clickable.
Created attachment 7697 Updated patch Updated patch. Nowadays I have no hard feelings about this, it's just an unpretentious suggestion to improve discoverability (three years ago I had to use google to find this out). The secondary icon still requires the user to hover the cursor for a moment, but I think is easier to find its tooltip than the entry itself. Clicking the button and get a popover would be even better, at the same time I think it would be clutter. Anyway, your call to pick or drop it.
Andre Miranda referenced this bugreport in commit f017232ee5a6f9fd9e49309b925ac0ae99c5ca47 clock: Improve discoverability of tooltip help-texts (Bug #11708) https://git.xfce.org/xfce/xfce4-panel/commit?id=f017232ee5a6f9fd9e49309b925ac0ae99c5ca47
Looks nice, thanks for rebasing and improving the patch!