Meaning of text between square brackets

Question

I have seen a lot of C# programs that use the [], for example [STAThread] and then the code follows. Another classic example is [DLLImport]

Answer 1

These are attributes.

Attributes have many uses - [Obsolete] marks a method as obsolete and the compiler will warn you. Others like [DebuggerNonUserCode] tell nothing to the compiler and are there to let the debugger know that the code in the marked method is auto-generated.

You can also create your own attributes and use them to mark any kind of metadata. For example, your Customer object might have an attribute [MarketingInformation("Customer is rich! Milk him good!")].