HHEADLINENO (HV218) reports the line number of the head of the household. According to the DHS recode manual:
This should always be 01; however, there are some households in certain surveys in which the head of household has not been listed as the first person in the household listing.
To determine the proportion of households (rather than persons in households) with a given characteristic (e.g., the share of households with electricity), researchers should restrict the sample of household members to one representative per household. Such restriction can be done by selecting only persons with line number 01 in the household roster (using HHLINENO) or selecting only persons coded as head of household in HHRELATE). HHEADLINENO demonstrates that these two criteria usually but not always identify the same person as a representative of the household.