There have been a couple of discussions recently on the mail list about mirroring and tiled pattern creation etc where the features being requested were already possible using the tile clones feature. Thought I’d try to expand on how to do them a bit as it seems to be something people consider to be voodoo. (true to me to an extent, so much power in there)
Anyways, first up is doing a mirror modifier
1) create a new document and turn the grid on, i set it to 25 and turned on snap nodes, and always snap.
2) Create a rectangle that covers half the page. I’ve filled it green just to make it nice and visible.
3) draw a squiggle over the rectangle, and group it.
4) Open the tile clones dialog, select reflect, and do 1 row, 2 columns.
5) Select the clone thats over the original, and delete it. you should get a full page with the left mirrored to the right.
6) enter the original group, delete the squiggle. I left the stroke on the box, but removed the fill as it makes it clear what the centerline for the mirror is. Tis a good idea to save the doc as something useful like mirror.svg if your going to want to create mirrored objects regularly. just open up that as a template and skip the first steps.
7) Make sure your still in the group(double click or right click > enter group), and then draw on the left side, and it will be instantly reflected on the right. be warned, if you overlap the clone will have a higher z-order so wierdness can ensue.
8) last thing was to remove the stroke from the box, I also shoved it one pixel toward the center as there are occasional rendering artifacts that leave a seam on what should be pixel perfect joins.
Hope thats clear enough.