An object o can have an internal public var myvar variable, and v:XML = classInfo.variable will correctly report it as a public variable, but o[ v.@name ] will fail because the variable is not available to us.
internal public var myvar
v:XML = classInfo.variable
o[ v.@name ]
This can be fixed in a similar way to the check for Transient metadata. An internal variable or accessor with have a uri attribute set to "http://www.adobe.com/2006/flex/mx/internal":
// If property is declared as internal, skip it
if ( v.@uri != '' && String(v.@uri).indexOf( "internal" ) != -1 )
I've implemented this on my fork: https://github.com/demauk/as3corelib/blob/master/src/com/adobe/serialization/json/JSONEncoder.as#L536