Design
The particular choice of character set selected for the 64 characters required for the base varies between implementations. The general rule is to choose a set of 64 characters that is both part of a subset common to most encodings, and also printable. This combination leaves the data unlikely to be modified in transit through information systems, such as email, that were traditionally not 8-bit clean. For example, MIME's Base64 implementation uses A–Z, a–z, and 0–9 for the first 62 values. Other variations, usually derived from Base64, share this property but differ in the symbols chosen for the last two values; an example is UTF-7.
The earliest instances of this type of encoding were created for dialup communication between systems running the same OS — e.g. uuencode for UNIX, BinHex for the TRS-80 (later adapted for the Macintosh) — and could therefore make more assumptions about what characters were safe to use. For instance, uuencode uses uppercase letters, digits, and many punctuation characters, but no lowercase, since UNIX was sometimes used with terminals that did not support distinct letter case.
Read more about this topic: Base64
Famous quotes containing the word design:
“Westerners inherit
A design for living
Deeper into matter—
Not without due patter
Of a great misgiving.”
—Robert Frost (1874–1963)
“To nourish children and raise them against odds is in any time, any place, more valuable than to fix bolts in cars or design nuclear weapons.”
—Marilyn French (20th century)
“Teaching is the perpetual end and office of all things. Teaching, instruction is the main design that shines through the sky and earth.”
—Ralph Waldo Emerson (1803–1882)