Hello @David Hockenbroch

I tested this simple method using CodeMode = Objectgenerator :

Method test() [ CodeMode = objectgenerator ]
{
    Write
    Quit 1
}

Do $SYSTEM.OBJ.Compile("User.NewClass1","ck")
We can see a lot of variable values at compile time :

....
%qstruct="ck"
....

%qstruct contains compile flags and qualifiers

Hi,

Two years ago, I analyzed the behaviours using stream and %Persistent class.  

Class Test.Stream1 Extends %Persistent
{

Property st As %GlobalBinaryStream;

ClassMethod add1() As %Status
{
	; write stream in ^Test.Stream1S
	Set o = ..%New()
	Do o.st.Write("azeruiop")
	Quit o.%Save()
}

ClassMethod add2() As %Status
{
	; write stream in ^CacheStream
	Set o = ..%New()
	Set st = ##class(%GlobalBinaryStream).%New()
	Do st.Write("azeruiop")
	Set o.st = st
	Quit o.%Save()
}

Storage Default
{
<Data name="Stream1DefaultData">
<Value name="1">
<Value>%%CLASSNAME</Value>
</Value>
<Value name="2">
<Value>st</Value>
</Value>
</Data>
<DataLocation>^Test.Stream1D</DataLocation>
<DefaultData>Stream1DefaultData</DefaultData>
<IdLocation>^Test.Stream1D</IdLocation>
<IndexLocation>^Test.Stream1I</IndexLocation>
<StreamLocation>^Test.Stream1S</StreamLocation>
<Type>%Storage.Persistent</Type>
}

}

The method add2 use ^CacheStream due to the default storage usage (as described by @Robert Cemper ).  

However, We can force the storage in ^Test.Stream1S with :
Do st.%LocationSet("^Test.Stream1S")