Tip from Alex W.
I'm sure convert line to shape has its uses. But why would anyone use it to give a line graduated fill/transparency when Contour keeps the line editable? It looks long and complicated but it' quite simple to understand.
1) Create your line (give it stroke and pressure profile if you want)
2) Give your line a one-step inner contour, with 0.01 width and milter join
3) Get rid of the think outline on your contour, but not the line. Details: Click on your newly created contour, make sure the status bar says "Contour", then give it "no outline" (i.e. right click the no color swatch)
4) Make your original line transparent. Details: Change to the selector tool. Click on the shape. If the status bar says "1 contour" press tab once so it says "1 line". Give this line 100% transparency)
5) Select the contour and give it whatever fill/transparency you want
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