PF keys like PFn, PA1, Attn generate an attention and are identified by the Attention IDentifier (AID).   To send PF keys you would execute:
PF(n) where n is the PF Key number you want to send.
Conceptually, all keystrokes are handled by the terminal to update the screen buffer.  When you want to send something to the host only specific keys generate that action.
So, letters, numbers, ... are local keystrokes
Keys like PFnn, PAn Attn Send the current buffer with an Attention Identifer AID that tells the host what “command” key was sent.
In this documentation script commands with an asterisk send data to the host.  The other keys simply update the local screen buffer.  (Pulled examples, see the doc for the full list)
*Enter    Enter AID (or send ASCII CR)
Erase erase previous character (or send ASCII BS)
EraseEOF  erase to end of current field EraseInput erase all input fields
Execute(cmd)  execute a command in a shell
FieldEnd  move cursor to end of field
FieldMark mark field
*Interrupt    send TELNET IP to host
Key(keysym)   insert key keysym Key(0xxx) insert key with character code xx
Left  move cursor left
*PA(n)    Program Attention AID (n from 1 to 3)
*PF(n)    Program Function AID (n from 1 to 24)