After starting to use Arch I switched to xterm and urxvt terminal and enjoyed the flexibility of them (esp. scaleHeight resource). However, I don't understand why sometimes configs work with "Xterm" and sometimes with "xterm" or "XTerm" (lower vs upper case "x" and"t").

For example, I have this odd config that is working on Ubuntu:

XTerm*faceName: terminus XTerm*faceSize: 11 XTerm*saveLines: 16384 XTerm*loginShell: true XTerm*charClass: 33:48,35:48,37:48,43:48,45-47:48,64:48,95:48,126:48 XTerm*termName: xterm-color XTerm*eightBitInput: false xterm*VT100.geometry: 100x80 <------ this line would not work with "Xterm" or "XTerm" XTerm*scaleHeight: 1.3 <----- but all others work with "XTerm" 

However, my Arch box runs on "xterm" fine. The same is true for URxvt terminal: I can't simply port my Arch .Xresources to Ubuntu14 work box because parts of it stop working, and I get different setups after running:

xrdb -merge .Xresources. 

x.org on xterm did not have any examples (searching for "xterm*" did not return anything on that page). I see examples with "Xterm", "xterm" and "XTerm" online... It baffles me that the config above works since it is syntactically off. Why is this the case? Does it maybe have something to do with new or old resources in X? Thanks!