Use this for inserting a single Unicode character as the appropriately converted UTF-8 sequences into the Debug Simulated World Input dialog.
Character Code
This is the code number of the Unicode character. It can be entered as decimal (0 to 2147483647) or hex (0 to 7FFFFFFF). You can look up the codes on an appropriate web site (or the Unicode 5 Standard book). For example, "Greek Small Letter MU" is 03BC.
Hex
Check to have the code entered interpreted as a hex number (this is the default, as this seems to be how Unicode codes are given). Otherwise it is interpreted as a decimal number.