-a symbol, an integer (or a cons of two integers or list of two integers),
-or a cons of two markers pointing to the same buffer.
-In the last case, the selection is considered to be the text
-between the markers.
-The data may also be a vector of valid non-vector selection values."
+a symbol, an integer (or a cons of two integers or list of two integers).
+
+The selection may also be a cons of two markers pointing to the same buffer,
+or an overlay. In these cases, the selection is considered to be the text
+between the markers *at whatever time the selection is examined*.
+Thus, editing done in the buffer after you specify the selection
+can alter the effective value of the selection.
+
+The data may also be a vector of valid non-vector selection values.
+
+Interactively, the text of the region is used as the selection value."