C# Language Specification

Reserved attributes

A small number of attributes affect the language in some way. These attributes include:

• 
  System.AttributeUsageAttribute (§17.4.1), which is used to describe the ways in which an attribute class can be used.
  
• 
  System.Diagnostics.ConditionalAttribute (§17.4.2), which is used to define conditional methods.
  
• 
  System.ObsoleteAttribute (§17.4.3), which is used to mark a member as obsolete.
  
• 
  System.Runtime.CompilerServices.CallerLineNumberAttribute, System.Runtime.CompilerServices.CallerFilePathAttribute and System.Runtime.CompilerServices.CallerMemberNameAttribute (§17.4.4), which are used to supply information about the calling context to optional parameters.
  

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