logging

type LogAppend struct {
	// Key is the name of the log field.
	Key string `json:"key,omitempty"`

	// Value is the value to use for the log field.
	// If it is a placeholder (with surrounding `{}`),
	// it will be evaluated when the log is written.
	// If the value is a key that exists in the `vars`
	// map, the value of that key will be used. Otherwise
	// the value will be used as-is as a constant string.
	Value string `json:"value,omitempty"`
}