Did you know that TRIM and EXTEND are two parts of one command, even though you can activate them separately?
When using Trim, hold down the Shift key and you’re in Extend mode; the current Cutting edges temporarily become Boundary edges. The converse is also true: in Extend, hold down Shift to Trim.
When in the TRIM or EXTEND command If you simply hit Enter when prompted to select Cutting or Boundary edges, ALL entities become edges, even entities within Blocks and Xrefs.
Edge mode allows you to Trim/Extend to implied edges. Implied edges are boundaries that would intersect your entities if the boundaries were long enough.
There are several ways to activate this feature:
1. Set system variable EDGEMODE = 1
2. When either command is active, press ENTER to activate nearest edge
When prompted with the following press E :
**(This will also set the system variable EDGEMODE to 1)**
Projection mode controls how trimming and extending behaves with 3D entities that don’t actually intersect, but appear to intersect, in various projections.
The setting projection mode is stored in the system variable PROJMODE and has the following values:
0 – True 3D mode (no projection)
1 – Project to the XY plane of the current UCS
2 – Project to the current view plane
This is activated by pressing ENTER when the TRIM or EXTEND command is already activated, and pressing P