I don’t unterstand \startfrontmatter, \starbodymatter etc.

I thought, the frontmatter has roman numerals, the bodymatter normal and 
so on. This is not automatically so. Now  founf how to make this, bus 
the problem is: I can’t reset the page number. I believed, it shoul 
work like this:

     \startfrontmatter
         \setupuserpagenumber[numberconversion=Romannumerals]
		% some stuff	
     \stopfrontmatter

     \startbodymatter
         \setupuserpagenumber[numberconversion=numbers]
         \setnumber[page]{1}
		%some stuff
	\stopbodymatter

This doesn’t work, may be because \setnumber is not a command in 
ConTeXt?

Where is my error?