In Unicode, a block is defined as one contiguous range of code points. Blocks are named uniquely and have no overlap. They have a starting code point of the form hhh0 and an ending code point of the form hhhF. A block explicitly can include code points that are unassigned and non-characters. Code points not belonging to any of the named blocks, e.g. in the unassigned planes 3–13, have the value block="No_block".
Conversely, every assigned code point has a property "Block name", which names in which block the character is. This is determined by the code point only, although a block name will have a descriptive nature: "Tibetan" or "Supplemental Arrows-A". All assigned code points have a single block name.
Subdivisions, such as "Chess symbols" in the block Miscellaneous symbols, are not a "block". The subgroup name is an informative editorial addition only.
The number of code points in a Unicode block is a multiple of 16. Unicode blocks range in size from the minimum of 16 to a maximum of 65,536 code points.
Unicode 9.0 defines 273 blocks: