What are the build setting modifiers in Xcode called?

I've seen some build settings being used like

$(PRODUCT_NAME:identifier)

Using :upper also makes the setting value uppercase, but I don't know what those are called and can't find any documentation. Does anyone know their name or where the documentation is to use them properly?

Solution

The file /Developer/Library/PrivateFrameworks/DevToolsCore.framework/Versions/A/DevToolsCore has a bunch of these:

[ 09:22 root@MacBookPro / ]# strings /Developer/Library/PrivateFrameworks/DevToolsCore.framework/Versions/A/DevToolsCore | egrep "(^:|^[a-z0-9]+$)"
:children.count=%lu
:name='%@'
:File='%@':Line=%lu:RefType=%@
:fileRef=%@:timestamp=%lu
:char-range=%@
:line-range=%@
:<range-type-%lu>=%@
:name='%@'
:name=%@:path='%@'
:name='%@'
:name='%@':buildSettings(%lu)=%@
:path='%@'
:quote
:identifier
:rfc1034identifier
:dir
:abs
:remoteRef='%@'
:File='%@':Head Revision=%@:Active Branch=%@
:scmProprties='%@':sandboxEntry='%@'
.... SNIP ....
upper
environment
diagnostics
type
category
description
path
kind
message
ranges
alternate
start
edges
location
file

Found this as well: DevToolsCore Framework Reference. Looks like an API for the Framework (- (id)initWithName:(id)arg1 productTypeIdentifier:(id)arg2).

Couldn't find any other documentation for it though, just this SO question (xcode-info-plist-build-variable-product-namerfc1034identifier-seems-complete).