Using Offset Path to Create a Mask
Use Offset Path and Paste in Front/Back to create masks easily.
Prepare Your Artwork
Start with the basics. Here we have an illustration of an elephant with linework to show its “wrinkles.” We want to confine the strokes to the body of the elephant but also be able to manipulate the linework later if we need to. You’ll do this by masking the linework using the elephant body as the clipping mask. Group the linework first so that it’s easy to select at any time. Select one of the strokes and then choose Select > Same > Stroke Color A. After all the strokes are selected, they are grouped (Cmd [Ctrl]-G) B.
Offset the Path
Now for the easy part—making the mask. Really. You first need to create a background element for the clipping mask. You could just make a large rectangle, but by using the existing elephant shape as your starting point, you can create a background shape that conforms to the mask, and in Outline view it will be more easily recognizable than a random rectangle that could very well be part of another object. Select the body of the elephant A and choose Object > Path > Offset Path B. In the dialog box enter 4 pt C to give yourself enough room to “play” with so that the object is easy to select and modify without the clipping mask that you will create later getting in the way. You’ve now created a slightly larger version of the elephant body that “bleeds” over but is below the stacking order of the shape of the original body D.
Make Your Mask
With the slightly larger version still selected, Shift-click the body so that both the offset path and the original elephant shape are selected A. Press Cmd (Ctrl)-7 (Make Clipping Mask) or use the contextual menu B, and that’s it! You’ve created a mask with an object below it that has the correct fill with a slight bleed.
Add the Linework
Now add the grouped linework. Just select the linework A and cut it to the clipboard. Then use the Direct Select tool and select the elephant body fill you just created B and press Cmd (Ctrl)-F to paste the linework in front of the elephant body. The linework is now inside the elephant clipping mask and has the added advantage of being able to be modified or moved at any time using the Direct Selection tool C. In the same way you can continually add other objects (such as the tip of the trunk) into the clipping mask using Paste in Front/Back D.