What does spans mean in the cell output?

[dipikakhullar]

Hi, these are some example cells from the TATR recognize model output:
35.420074462890625,
474.67864990234375,
47.1126594543457],
'column_nums': [5],
'row_nums': [1],
'column header': True,
'subcell': False,
'projected row header': False,
'cell text': 'max',
'spans': [],
'bbox_input': [501.5734062194824,
281.6884765625,
527.1918754577637,
293.3810615539551]},

{'bbox': [242.34381103515625,
10.655202865600586,
336.2829284667969,
47.1126594543457],
'column_nums': [3],
'row_nums': [0, 1],
'column header': True,
'projected row header': False,
'cell text': 'Max. Thickness (T) mm/inches',
'spans': [],
'bbox_input': [294.8570365905762,
256.92360496520996,
388.7961540222168,
293.3810615539551]},

I have a few questions:

1. what does "spans" mean? When is spans non empty? Any example?
2. Is there a concept of row spans and column spans?
3. what is 'projected row header'?
4. What is 'column header'? And how does this differ from 'projected row header'?