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If you want to add or change characters on the section line, use the General and Text pages of the section line's Properties. See See Properties of Section Lines.
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Note: that there is a difference between a section and a sectional view. The 3D function Section (see Sectioning Solids) creates an actual section of a 3D object, whereas a sectional view is what you see when looking in the direction of the section line.
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