Why does HEW allow Software Breakpoints in ROM space ?

I am using following Tools Renesas High Performance Embedded Workshop(HEW) Version 4.09. Renesas E8a Emulator IAR Compiler My target board is wired with Renesas M16C/6N5 Group Microcontroller. This microcontroller has 128K bytes of internal flash from 0xE0000 - 0xFFFFF. Why does HEW allow me to put breakpoints in this address range? I click on S/W Breakpoints column which is on left of source window to set my breakpoints. The way software breakpoints work is that they actually modify the instruction. You can't modify contents of ROM. Then, how are S/W breakpoints getting set in internal flash space? Thank you!