**head**-
Start-point of a hypertext link. Equivalent to the source of a link. Points to the tail.

**here()**-
- In an XPointer expression, indicates the current node.

**hexadecimal**-
The base 16 notation for representing numeric values. In this notation there are 16 value symbols in place of the normal 10. The first 10 are the same, '0' to '9', and the letters 'A' to 'F' represent the additional six values. A = 10, B = 11, C = 12, D = 13, E = 14 and F = 15. Hexadecimal is popular in computing because base 16 is a multiple of two, so is a simple multiple of binary, or base 2. Four bits can represent values between zero ('0000' in binary) and 15 ('1111' in binary), which can be represented by a single hexadecimal digit. Two digits are required to represent ...

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