Does the "Data" field in ETH transactions have to be in hex?

In MEW (and other ETH wallets) there is the option to add hex data to a TXN. Does that data have to be HEX? What would happen if I entered Hello World there? Would it just get converted to 0x48656c6c6f20576f726c64 or is there some type of data structure / convention for this field for encoding string / int / long / struct data?

submitted by /u/brianddk