add attribute to cell

How would one add a tag or other attribute to a cell?

For example, if the cell at (2,3) is blank, I want to add an attribute
called "tag" or "info" that says "thisFieldWasBlank"

Later, when I go to cell (2,3) I can check the attribute in some manner
obj.cellGetAttribute("tag")

You should create new property in the cell model with defineCellProperty() method -

// define new cell property
obj.defineCellProperty("tag");

// assign the property value
obj.setCellTag("abc", 2, 3);

// retrieve the property value
alert(obj.getCellTag(2, 3));

- getCellTag() and setCellTag() methods will be created automatically by defineCellProperty("tag") call.