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Give a name to byte and code point's underlying number #305

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May 18, 2020
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Give a name to byte and code point's underlying number #305

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459d58e
Give a name to byte and code point's underlying number
annevk May 15, 2020
16091d4
require more precision
annevk May 16, 2020
5aa6822
align byte a bit more with code point
annevk May 18, 2020
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21 changes: 14 additions & 7 deletions infra.bs
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Expand Up @@ -442,8 +442,11 @@ JavaScript <b>null</b> value. [[!ECMA-262]]

<h3 id=bytes>Bytes</h3>

<p>A <dfn export>byte</dfn> is a sequence of eight bits, represented as a double-digit hexadecimal
number in the range 0x00 to 0xFF, inclusive.
<p>A <dfn export>byte</dfn> is a sequence of eight bits, represented as two
<a>ASCII upper hex digits</a>, in the range 0x00 to 0xFF, inclusive. A <a>byte</a>'s
<dfn for=byte>value</dfn> is its underlying number.

<p class=example id=example-byte-value>0x40 is a <a>byte</a> whose <a for=byte>value</a> is 64.

<p>An <dfn export>ASCII byte</dfn> is a <a>byte</a> in the range 0x00 (NUL) to 0x7F (DEL),
inclusive. As illustrated, an <a>ASCII byte</a>, excluding 0x28 and 0x29, may be followed by the
Expand Down Expand Up @@ -535,14 +538,17 @@ contains, in the range 0x61 (a) to 0x7A (z), inclusive, by 0x20.

<p>To <dfn export>isomorphic decode</dfn> a <a>byte sequence</a> <var>input</var>, return a
<a>string</a> whose <a for=string>code point length</a> is equal to <var>input</var>'s
<a for="byte sequence">length</a> and whose <a>code points</a> have the same values as
<var>input</var>'s <a>bytes</a>, in the same order.
<a for="byte sequence">length</a> and whose <a>code points</a> have the same
<a for="code point">values</a> as the <a for=byte>values</a> of <var>input</var>'s <a>bytes</a>, in
the same order.


<h3 id=code-points>Code points</h3>

<p>A <dfn export lt="code point|character">code point</dfn> is a Unicode code point and is
represented as a four-to-six digit hexadecimal number, typically prefixed with "U+".
represented as "U+" followed by four-to-six <a>ASCII upper hex digits</a>, in the range U+0000 to
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Is this too circular? Not really sure how else to do this.

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Maybe do it the other way around? Perhaps:

A code point is a Unicode code point, whose value is an integer between 0 and 0x10FFFF inclusive and represented as the string U+ followed by four to six ASCII upper hex digits.

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I think that still has the same issue, as ASCII upper hex digits are defined using the U+ convention.

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Avoiding the circularity seems like it would lead to double-defining ASCII upper hex digits and reduce the overall clarity. I don't think people have a hard time with the U+ syntax so much as they have a difficult time with the difference between USVs/code points vs. code units (particularly the UTF-16 variety).

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I don't think we can really avoid circularity in Infra without making it significantly more opaque. See previous discussions at #230 (comment)

U+10FFFF, inclusive. A <a>code point</a>'s <dfn for="code point">value</dfn> is its underlying
number.

<p>A <a>code point</a> may be followed by its name, by its rendered form between parentheses when it
is not U+0028 or U+0029, or by both. Documents using the Infra Standard are encouraged to follow
Expand Down Expand Up @@ -759,8 +765,9 @@ ordering will not match any particular alphabet or lexicographic order, particul
<li><p><a>Assert</a>: <var>input</var> contains no <a>code points</a> greater than U+00FF.

<li><p>Return a <a>byte sequence</a> whose <a for="byte sequence">length</a> is equal to
<var>input</var>'s <a for=string>code point length</a> and whose <a>bytes</a> have the same values
as <var>input</var>'s <a>code points</a>, in the same order.
<var>input</var>'s <a for=string>code point length</a> and whose <a>bytes</a> have the same
<a for=byte>values</a> as the <a for="code point">values</a> of <var>input</var>'s
<a>code points</a>, in the same order.
</ol>

<hr>
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