nh_table: The name of the NHANES table that contains the desired variable.
colname: The name of the table column (variable).
dxa: If TRUE then the 2005-2006 DXA codebook will be used (default=FALSE).
Returns
The codebook is returned as a list object. Returns NULL upon error.
Details
Each NHANES variable has a codebook that provides a basic description as well as the distribution or range of values. This function returns the full codebook information for the selected variable. If the environment variable NHANES_TABLE_BASE
was set during startup, the value of this variable is used as the base URL instead of https://wwwn.cdc.gov (this allows the use of a local or alternative mirror of the CDC documentation).