interop/attribute: update documentation

pkg/interop/attribute/attribute.go

@@ -1,17 +1,65 @@
+/*
+Package attribute provides getters for transaction attributes.
+*/
 package attribute
 
-// Package attribute provides function signatures that can be used inside
-// smart contracts that are written in the neo-go framework.
-
-// Attribute stubs a NEO transaction attribute type.
+// Attribute represents transaction attribute in Neo, it's an opaque data
+// structure that you can get data from only using functions from this package.
+// It's similar in function to the TransactionAttribute class in the Neo .net
+// framework. To use it you need to get is first using transaction.GetAttributes.
 type Attribute struct{}
 
-// GetUsage returns the usage of the given attribute.
+// GetUsage returns the Usage field of the given attribute. It is an enumeration
+// with the following possible values:
+//      ContractHash   = 0x00
+//      ECDH02         = 0x02
+//      ECDH03         = 0x03
+//      Script         = 0x20
+//      Vote           = 0x30
+//      CertURL        = 0x80
+//      DescriptionURL = 0x81
+//      Description    = 0x90
+//
+//      Hash1  = 0xa1
+//      Hash2  = 0xa2
+//      Hash3  = 0xa3
+//      Hash4  = 0xa4
+//      Hash5  = 0xa5
+//      Hash6  = 0xa6
+//      Hash7  = 0xa7
+//      Hash8  = 0xa8
+//      Hash9  = 0xa9
+//      Hash10 = 0xaa
+//      Hash11 = 0xab
+//      Hash12 = 0xac
+//      Hash13 = 0xad
+//      Hash14 = 0xae
+//      Hash15 = 0xaf
+//
+//      Remark   = 0xf0
+//      Remark1  = 0xf1
+//      Remark2  = 0xf2
+//      Remark3  = 0xf3
+//      Remark4  = 0xf4
+//      Remark5  = 0xf5
+//      Remark6  = 0xf6
+//      Remark7  = 0xf7
+//      Remark8  = 0xf8
+//      Remark9  = 0xf9
+//      Remark10 = 0xfa
+//      Remark11 = 0xfb
+//      Remark12 = 0xfc
+//      Remark13 = 0xfd
+//      Remark14 = 0xfe
+//      Remark15 = 0xff
+// This function uses `Neo.Attribute.GetUsage` syscall internally.
 func GetUsage(attr Attribute) byte {
 	return 0x00
 }
 
-// GetData returns the data of the given attribute.
+// GetData returns the data of the given attribute, exact interpretation of this
+// data depends on attribute's Usage type. It uses `Neo.Attribute.GetData`
+// syscall internally.
 func GetData(attr Attribute) []byte {
 	return nil
 }