Re: What is the "meaning" of an XML entity? of a character entity?

On Thu, 19 May 2022 at 11:25, Roger L Costello <[email protected]> wrote:

> Hi Folks,
>
> Consider this XML entity:
>
>         &amp;
>
> What is its meaning?
>

I am not sure it has a meaning, and it is an entity reference not an entity,



>
> Answer: its meaning is & and &amp; is literal syntax.
>

Entities have Replacement  texts (not meanings), The replacement text of
amp is pre-defined by XML and is

&#38;#38;

(not &)

See https://www.w3.org/TR/xml/#sec-predefined-ent




> The meaning of this character entity:
>
>         &#x41;
>

that is not an entity reference at all, it is a character reference. It
doesn't reference an entity that holds a replacement text, it is replaced
inline by the referenced character.



> is A and &#x41; is literal syntax.
>



>
> Recall that in a parser there are two stages to processing an input string:
>
> input string --> lexical analysis (lexer) --> syntax analysis (parser)
>
> The lexer groups the characters in the input string into tokens and sends
> the tokens to the parser.
>
> Flex is a lexer-generator, i.e., the output of Flex is a lexer.
>
> In the Flex manual [1] it recommends on page 76 that a lexer be designed
> to send the meaning of an entity to the parser, not the literal syntax,
> i.e.,
>
> &amp; --> lexer --> & --> parser
>
> Pretty interesting, I think.
>

Entity and character references are expanded at different times.

After

<!ENTITY foo "aaa &lt; bbb">

the entity foo has replacement  text "aaa &lt; bbb" as the reference to the
entity lt; is not expanded while defining foo.

But

<!ENTITY foo "aaa &#60; bbb">

is a syntax error as &#60; is replaced while reading the definition so this
is

<!ENTITY foo "aaa <  bbb">

with a non-well formed start tag,

David


>
> /Roger
>
> [1] Flex manual is here:
> https://epaperpress.com/lexandyacc/download/flex.pdf
>
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