Editing Module:Val/units/doc (section)

=== Fourth field flags ===
The module must be told directly about sorting factors, spacing, and aliasing for a unit code.

There is an optional field that goes at the end after two or more spaces or one or more tabs.  It is a flag mainly used to provide for that unit to be sorted in a table. 
Flags are mainly for sorting, and they work for either record type. Just add two or more spaces, or one or more tabs, and then the flag field.  (Optional flags ALIAS and NOSPACE and ANGLE are for even more advanced users.  See [[#Advanced unit flags|&sect;Advanced unit flags]] below.)

Using SI requires that the unit symbol compare precisely to the unit code, and so never allows HTML or other characters in the symbol.  Any difference between the unit symbol and unit code must be an SI prefix, such as k, M, or G.