Editing Module:Val/units/doc (section)

== Advanced unit flags ==

You can alias Convert or Val units.  But these are different things.
* A "unit code alias" is when the same ''unit pagename and unit symbol'' are defined twice. If a different ''unit code'' is assigned to the same unit symbol and unit pagename, (say, as a copy of the previous entry) it will work as a Val alias.  

* A "unit alias" is when Val alias a Convert unit code. A unit of measurement is ''here'' denoted ALIAS to mean "they are defined ''there''".  Val ''defaults'' to Convert, but it's good to this explicit for certain Val units: the ones tempting to define here, but that you don't want defined here because, says ALIAS, they are ''already'' defined there.
* If your unit code is not listed at {{tl|Val/list}}, you can check for it at {{tl|Convert#Units}}

For spacing and aliasing: 
*<code>ALIAS</code> specifies that the unit's symbol is the code for a unit defined in {{tlf|convert}}}.
*<code>NOSPACE</code> prevents the default insertion of a non-breaking space before the unit symbol.

*If you see the <code>ANGLE</code> flag, this identifies those special units that must displayed not only after the main Val number, but also after its [[uncertainty#Measurements]] numbers.(<code>ANGLE</code> also implies <code>NOSPACE</code>.)