You are typing the argument to a command. 
These commands are available here: 
 
Return	Enter the line. 
Escape	Fill in the default string, if any, as shown within 
	parentheses. Only works at the beginning of the line. 
^F	Fill in the current filename. 
^G	Abort this. 
^Q	Insert the next character. (Quoting ^@ won't work). 
^U	Rub out the whole line back to the prompt. 