aria-colindex property is used on a table, grid or a treegrid where all the columns are currently not present. aria-colindex property notifies the index or position of the column in a table or grid or a treegrid with respect to the number of columns available. User agents can calculate the index of the column if all the columns of the table or grid are available, so aria-colindex property is not required in those cases.
The value of aria-colindex property must be greater than or equal to one, greater than the value of previous colindex in the same row and less than or equal to total number of columns in the table. For a cell or gridcell that spans more than one column set aria-colindex property at the beginning of the cell. If the set of columns which is present in the DOM is contiguous, and if there are no cells which span more than one row or column in that set, then authors may place aria-colindex on each row, setting the value to the index of the first column of the set.
Also see similar aria-colcount property
aria-colindex property used in roles
Values of aria-colindex property
The value of aria-colindex property must be greater than or equal to one, greater than the value of previous colindex in the same row and less than or equal to total number of columns in the table.