For Build setting syntax, refers to http://disanji.net/iOS_Doc/#documentation/DeveloperTools/Conceptual/XcodeBuildSystem/300-Build_Settings/bs_build_settings.html
For all the build setting variables, refers to http://developer.apple.com/library/mac/#documentation/DeveloperTools/Reference/XcodeBuildSettingRef/1-Build_Setting_Reference/build_setting_ref.html
To reference a build setting value in a build setting specification, use the name of the build setting surrounded by parentheses and prefixed by the dollar-sign character ($). For example, the specification of a build setting that refers to the value of the Product Name build setting could be similar to
The name of this target's product is $(PRODUCT_NAME).