context_builder.go
func (cb *ContextBuilder) SetFormat(f Format) *ContextBuilder {
	if cb.CallOptions == nil {
		cb.CallOptions = new(CallOptions)
	}
	cb.CallOptions.Format = f
	return cb
}
func (cb *ContextBuilder) SetFormat(f Format) *ContextBuilder {
	if cb.CallOptions == nil {
		cb.CallOptions = new(CallOptions)
	}
	cb.CallOptions.Format = f
	return cb
}
// SetFormat sets the Format call option ("as" transport header).