This value set includes codes based on the following rules:

• Include these codes as defined in http://terminology.hl7.org/CodeSystem/v3-TimingEvent

  Code	Display	Definition
  ACD	ACD	before lunch (from lat. ante cibus diurnus)
  ACM	ACM	before breakfast (from lat. ante cibus matutinus)
  ACV	ACV	before dinner (from lat. ante cibus vespertinus)
  HS	HS	**Description:** Prior to beginning a regular period of extended sleep (this would exclude naps). Note that this might occur at different times of day depending on a person's regular sleep schedule.

• Include these codes as defined in http://terminology.hl7.org/CodeSystem/v3-NullFlavor

  Code	Display	Definition
  UNK	Unknown	**Description:**A proper value is applicable, but not known. **Usage Notes**: This means the actual value is not known. If the only thing that is unknown is how to properly express the value in the necessary constraints (value set, datatype, etc.), then the OTH or UNC flavor should be used. No properties should be included for a datatype with this property unless: 1. Those properties themselves directly translate to a semantic of "unknown". (E.g. a local code sent as a translation that conveys 'unknown') 2. Those properties further qualify the nature of what is unknown. (E.g. specifying a use code of "H" and a URL prefix of "tel:" to convey that it is the home phone number that is unknown.)