The act of selecting a block of text to replace or to surround with an element is performed the same in Vex as in most word processors: by moving the caret while holding the Shift key or by dragging the mouse between two positions. The main difference is that in some cases, Vex will expand the selection so that it does not span only a portion of an element.
To see this in action, place the caret in the middle of an inline element containing some text. While holding the Shift key, move the caret towards the end of the element. As the caret passes the end marker for the element, note that the starting point of the selection jumps to the start of the element. If you move the caret back inside the element (while still holding Shift), you'll notice that the start of the selection jumps back to its original place.
When a block element is selected, Vex draws an outline around the entire block, showing the element name in the lower right corner. This allows you to see that the entire element is selected rather than just its contents.
This selection behaviour is Vex's way of preserving the structure of the document. It is based on the assumption that normally you want to manage entire elements.
