Drag on empty page and a rubber band gathers every mark it sweeps over.
Touching counts rather than enclosing: a band you have to draw right
around a long arrow is a band you draw twice. Shift-click adds or removes
one, Ctrl+A takes the page.
What the group can then do is move, restyle, duplicate and delete, each as
a single undo step — six marks deleted is one thing the user did, so it
has to be one thing to undo. The selection bar offers only what is true of
every member: a group of shapes gets Fill, a group of stamps gets size and
weight, a mixed group gets neither, and none of them gets Edit, which
needs one mark to put a caret in.
No resize handles on a group. Stretching a mixed selection means deciding
what a stretch does to text, which scales by font size, and to a line,
which has no box at all; until there is an answer worth defending,
offering the grip would promise something this cannot keep.
Each member is outlined as well as the group, because a band that caught
one more mark than you meant is worth seeing before you press Delete.
A group lives on one page. A mark carries its page, and PDF user space
means nothing across two of them, so a band selects within the page it
was drawn on.
One trap found on the way: starting the band on a press means calling
preventDefault, which is also what gives a form field its caret — so the
band now keeps its hands off the annotation layer, and typing into a PDF
form still works.