If you’ve ever tried to get at the requisition history, you’ll be aware of the WorkActionNumber that tells you what the event in the history is. The big issue is that even if you do an export on this table, it doesn’t give you all the elements (I have no idea why).
So here is the list in it’s full glory for your reference pleasure:

NumberDescription
1New
2Delete
3Add Comments
4Request Contribution
5Return my Contribution
6Put on Hold
7Reactivate
8Save as Open
9Cancel Requisition
10Request Approval
11Reject
12Approve
13Terminate Approval Process
14Request Sourcing Configuration
16Fill
17On Scheduled event
18Posting and Sourcing…
19On UnPosted event
20On Expired event
21On Ownership modification
22Approve – Final
23Deny – Final
24On Extend
25On Hire
26On Duplicate
27OnEndOfPostingWarning
28On Hiring Manager modification
29On Hiring Manager not specified
30OnPostRecruitUSA
31OnUnpostRecruitUSA
32OnUpdateRecruitUSA
33OnUnhire
34Reopen Requisition
35Amend Approval Path
36Request Approval Path Amendment
37On Add Approvers
38On Remove Approvers
39Pass
40Pending
41On Update Approval Recipient
42On New Requisition Number
43On Update Requisition Number
44On Remove Requisition Number
45On Cost Center Entry
46On Cost Center Modification
47On Cost Center Deletion
49Selection workflow changed
50Decide on Approval
51OnPostEquest
52OnUnpostEquest
53OnUpdateEquest
54On Department Modification
55On Department Deletion
56Prevent Posting
57Allow Posting
58On last position accepted
59On number of position change
60On start date updated
61On Delayed Posting event
62On Expired Event (Not Trackable)
63Attach File
64Delete File
65On Recruiter Assistant modification
66On Hiring Manager Assistant modification
67On Add Collaborators
68On Remove Collaborators
69On Remove Hiring Manager Assistant
70On Remove Recruiter Assistant
71On Site Assigned
72On Site Deleted
73On Job Role Assigned
74On Job Role Deleted
75Send an approval request reminder