Re: Weird XML rules

On Sat, 19 Mar 2022 at 13:45, Roger L Costello <[email protected]> wrote:

> On Thursday, Liam Quin wrote:
>
> > numeric character references are always treated as data when they are
> read, not markup.
>
> If the word "numeric" is removed from that sentence does the sentence
> still hold true? That is, _all_ character references are treated as data,
> not markup. True?


there are no non numeric character references, just decimal or hex numeric.


> For example, just as the numeric character reference &#x3C; is always
> treated as data, so too the XML character reference &lt; is always treated
> as data. What that means is:
>

&lt;  isn't a "character reference"  it's an entity reference to an
internal entity which in that case is defined as

<!ENTITY lt     "&#38;#60;">


so the entity value is the character reference &#60;

Internal entities in general expand to markup, if you have

<!ENTITY foo "<b>bar</b>">

then &foo; will eventually parse as the element b with content foo. So &lt;
is not interpreted as markup not because it is an entity reference but
because its replacement text is a character reference.





> <Test foo="&#x3C;"/>
> <Test foo="&lt;"/>
>
> are both legal.
>
> To an XML-aware tool, the following all denote the same character. More
> precisely, they all denote the same code point.
>
> <
> &lt;
> &#x3C;
> &#x3c;
> &#x60;
>
> And yet, they are treated differently:
>
> < is illegal in an attribute value because < is treated as markup. But the
> entity versions are legal in an attribute value because they are treated as
> data.
>
> < is illegal in an element value because < is treated as markup. But the
> entity versions are legal in an element value because they are treated as
> data.
>
> Is this correct?
>
> So, the same character is treated differently purely because of the way
> the character is lexically represented.
>
> Isn't that weird?
>

No. Isn't that expected and similar to any other markup or programming
language, all of which have ways to access the characters used as syntax
just as normal characters in strings?



>
> Is there ever a case where an entity version is not treated as data;
> rather, it is treated as markup?
>

the replacement text of entity references  are always parsed as markup. In
the case of lt the markup is &#60; so produces the character <



> /Roger
>
>
David


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