 Within the range of mass-classifiers, authors have proposed subdivisions based on the manner in which a mass-classifier organizes the noun into countable units. One of these is measurement units (also called "standard measures"), which all languages must have in order to measure items; this category includes units such as kilometers, liters, or pounds (see list). Like other classifiers, these can also stand without a noun; thus, for example, 磅 (bàng, pound) may appear as both 三磅肉 (sān bàng ròu, "three pounds of meat") or just 三磅 (sān bàng, "three pounds", never * 三个磅 sān ge bàng). Units of currency behave similarly: for example, 十元 (shí yuán, "ten yuan"), which is short for (for example) 十元人民币 (shí yuán rénmínbì, "ten units of renminbi"). Other proposed types of mass-classifiers include "collective" mass-classifiers, such as 一群人 (yì qún rén, "a crowd of people"), which group things less precisely; and "container" mass-classifiers which group things by containers they come in, as in 一碗粥 (yì wǎn zhōu, "a bowl of porridge") or 一包糖 (yì bāo táng, "a bag of sugar").
