[SDPhantom]

There are quirks in how Lua stores tables internally. Every table is created with 2 data arrays, one for sequential data and another for associative data. Sequential data is stored when you assign a non-nil value to the next index in a table, this index is equal to #t+1. If you assign data to a key that is greater than the next index or is a non-number, the data is stored in the associative array. Both the length operator and ipairs() operate exclusively off the sequential array.

The table constructor { } breaks this rule in its own way in which undefined keys are written directly into the sequential array and may include embedded nils. The table constructor also trims any nils from the right side of the list.

There is another quirk in Lua that allows you to manually force nils to be embedded into the sequential array of a table. This is done by inserting two non-nil values then overwriting the first with nil.