mention app.Preprocessor in implementations of it

cmd/bytemark/app/flags/account_name.go

@@ -20,7 +20,8 @@ func (name *AccountNameFlag) Set(value string) error {
 }
 
 // Preprocess sets the value of this flag to the global account flag if it's unset,
-// and then runs lib.ParseAccountName
+// and then runs lib.ParseAccountName. This is an implementation of `app.Preprocessor`,
+// which is detected and called automatically by actions created with `app.Action`
 func (name *AccountNameFlag) Preprocess(c *app.Context) (err error) {
 	if name.Value == "" {
 		name.Value = c.Context.GlobalString("account")

cmd/bytemark/app/flags/group_name.go

@@ -19,6 +19,9 @@ func (name *GroupNameFlag) Set(value string) error {
 
 // Preprocess defaults the value of this flag to the default group from the
 // config attached to the context and then runs lib.ParseGroupName
+// This is an implementation of `app.Preprocessor`, which is detected and
+// called automatically by actions created with `app.Action`
+
 func (name *GroupNameFlag) Preprocess(c *app.Context) (err error) {
 	if name.GroupName != nil {
 		c.Debug("GroupName.Preprocess before %#v", *name.GroupName)

cmd/bytemark/app/flags/privilege.go

@@ -78,6 +78,8 @@ func (pf *PrivilegeFlag) Set(value string) (err error) {
 
 // Preprocess parses the Privilege and looks up the target's ID so it can
 // be made into a brain.Privilege
+// This is an implementation of `app.Preprocessor`, which is detected and
+// called automatically by actions created with `app.Action`
 func (pf *PrivilegeFlag) Preprocess(c *app.Context) (err error) {
 	args := privArgs(strings.Split(pf.Value, " "))
 

cmd/bytemark/app/flags/virtual_machine_name.go

@@ -19,6 +19,8 @@ func (name *VirtualMachineNameFlag) Set(value string) error {
 
 // Preprocess defaults the value of this flag to the default server from the
 // config attached to the context and then runs lib.ParseVirtualMachineName
+// This is an implementation of `app.Preprocessor`, which is detected and
+// called automatically by actions created with `app.Action`
 func (name *VirtualMachineNameFlag) Preprocess(c *app.Context) (err error) {
 	if name.Value == "" {
 		return