Assignment Candidate is a user who is able to get the task (assign it to herself).
One task can have multiple Assignment Candidates but only one becomes assignee of the task.
Assignment Candidate views the task in "Available tasks" list on Tasks screen.
Assignment Candidate can:
open available task
view task description
view data form
change due date
assign/reassign the task
But she cannot :
fill editable form fields,
complete the task
reopen completed task
till she becomes assignee for the task.
If Assignment Candidate assigns the task to herself, this task moves to "My tasks" list on Tasks screen ("Active" tasks filter should be used).