Hello again,

OVERRIDES (and overrides in general) is a bit tersely documented at the moment. Here's a suggestion for a new version that includes some examples, mentions standard override-related variables, and explains the _pn-${PN} override:

  OVERRIDES:
    A colon-separated list of overrides that currently apply. Overrides are a
    BitBake mechanism that allows variables to be selectively overridden at the
    end of parsing. The set of overrides in OVERRIDES is meant to represent
    the "state" during building, including the current recipe being built, the
    machine it is being built for, etc.
    
    As an example, if the string "an-override" appears as an element in the
    colon-separated list in OVERRIDES, then the following assignment will
    override FOO with the value "overridden" at the end of parsing:
  
      FOO_an-override = "overridden"
  
    See the "Conditional Syntax (Overrides)" section of the BitBake User Manual
    for more information on the overrides mechanism.
  
    The default value of OVERRIDES includes the values of the [CLASSOVERRIDE],
    [MACHINEOVERRIDES], and [DISTROOVERRIDES] variables. Another important
    override included by default is pn-${PN}. This override allows variables
    to be set for a single recipe within configuration (.conf) files, like in
    the following example:
  
      FOO_pn-myrecipe = "myrecipe-specific value"
  
    An easy way to see what overrides apply is to search for OVERRIDES in the
    output of
    [bitbake -e](http://www.yoctoproject.org/docs/2.2/ref-manual/ref-manual.html#usingpoky-debugging-viewing-variable-values).


In addition, the following note could be added to the end of the PREFERRED_VERSION glossary entry:

  Note {
  The _forcevariable override is not handled specially. It only works because
  the default value of [OVERRIDES] includes "forcevariable".
  }


Cheers,
Ulf