Partial matches to the item value are handled by calling pmatch(). This
can be convenient, with item="tem" and item="temperature" having the same
effect. However, it can also be confusing for labels that are similar.
For example, there are 5 variants of oxygen concentration.
It is best to unabbreviated values, especially in non-interactive work.
The list of known values is:
"absolute salinity", "along-spine distance km", "along-track distance km",
"C", "conductivity mS/cm", "conductivity S/m", "conservative temperature",
"CT", "depth", "direction", "distance", "distance km", "eastward",
"elevation", "fluorescence", "frequency cph", "heading", "latitude",
"longitude", "N", "N2", "nitrate", "nitrite", "northward", "oxygen",
"oxygen mL/L", "oxygen saturation", "oxygen umol/kg", "oxygen umol/L",
"p", "phosphate", "pitch", "roll", "S", "SA",
"sigma0", "sigma1", "sigma2", "sigma3", "sigma4",
"sigmaTheta",
"silicate", "sound speed", "spectral density m2/cph", "speed",
"spice", "spiciness0", "spiciness1", "spiciness2",
"T", "theta", "tritium", "u", "v", "w", and "z".