The <remarks> section in the definition of the origin= attribute of the <timeline> element are at best confusing, at worst nonsense. It says “If the absolute value for the time of origin is not known, an arbitrary time (such as 00:00) should be used.”. Used where? On this attribute? Its datatype is data.pointer — putting “00:00” on the value of origin= of <timeline> suggests that the origin time is found as the root element of a file named “00:00” in the same directory as the current file (whose root had better be a <when>, I guess). As the absolute= of the <when> to which this <origin> points? If so, the datatype of absolute= of <when> is data.temporal.w3c, so “00:00” is not a valid value, and would mean midnight in any case.