How can I see the escape sequence of a given key combo (specifically Alt+letter) when I use the meta8 option in URxvt?

Question

My ~/.Xdefaults does not contain this like

URxvt*meta8: true

and if I open Vim and hit Ctrl+v and then Alt+j, I get this

^[j

where ^[ occupies two characters but is in reality a single entity representing the escape character.

If I do put that line in my ~/.Xdefaults, then if I hit Ctrl+vAlt+j, nothing happens; if afterwards I hit

• SpaceSpace (yeah, twice) I get ê (hex code 00ea);
• if I hit yz, I get the same;
• even Alt+jAlt+j gives the same.

But it's not always like that. If after Ctrl+vAlt+j I

• hit ArrowUp I get êA
• hit ArrowDown I get êB
• hit ArrowRightI get êC
• hit ArrowLeft I get êD

and I think the reason is that all of Space, y, z, Alt+j are... 1-or-2-bytes sequences, whereas all of ArrowUp, ArrowDown, ArrowRight, ArrowLeft are longer? What I mean is that I press Ctrl+v before each of them when I don't have the meta8 option enabled, I get

• Space
• y y
• z z
• Alt+j j
• ArrowUp OA
• ArrowDown OB
• ArrowRight OC
• ArrowLeft OD

so it's a bit like Ctrl+v is waiting for just 1 or 2 bytes when meta8 is disabled, and is waiting for more when it is enabled?