Help appreciated in helping me find how to avoid a tedious-to-fix error. 
Question 1: In Attribute Objects, what is /O?
Question 2: Based on the following, how could I have introduced error?
I had a table 9 columns wide with two header rows for the last 6 columns. Cells were overlapping in the Table Editor view, so I edited the attributes (Edit Attribute Objects from the tags pane) to include appropriate Col and RowSpans. All scopes were Column. My table was still marked as irregular and looked a mess in PAC 3. I finally noticed that the first two columns had an /O attribute of Layout, while all others had the attribute of Table. Everything was fine when those values were changed to Table as well. Looking at a previous document backup, there were no items in the Attribute Object area for these cells, so somewhere between versions there was some user error.
While trying to find my own answer to how I screwed up, I came across this page: Edit document structure with the Content and Tags panels (Adobe Acrobat Pro) , Set ColSpan and RowSpan attributes. The thing is that I didn't enter /O attributes for any of the TH cells, yet all but the first two already had the correct values.
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