Hello, I would like to report an issue because of incorrect DTD handling.

This is a well-formed and valid XML document.

<?xml version="1.0"?>
<!-- sample.xml -->
<!DOCTYPE root [
        <!ENTITY ent ">">
        <!ELEMENT root (#PCDATA)>
]>
<root>&ent;</root>

For the above XML document, write the following simple code,

use quick_xml::{Reader, events::Event};

fn main() {
    let path = std::env::args().nth(1).unwrap();
    let mut reader = Reader::from_file(path).unwrap();
    let mut buf = vec![];
    while reader.read_event_into(&mut buf).unwrap() != Event::Eof {}
}

and run it

cargo run -- sample.xml

As a result, Reader::read_event_into panics with the following message.

thread 'main' (427815) panicked at src/main.rs:7:44:
called `Result::unwrap()` on an `Err` value: Syntax(InvalidBangMarkup)
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

Furthermore, the following XML document is also well-formed.

<?xml version="1.0"?>
<!-- sample.xml -->
<!DOCTYPE root [
        <!ENTITY ent "<">
]>
<root />

The execution results for this are as follows.

thread 'main' (435643) panicked at src/main.rs:7:44:
called `Result::unwrap()` on an `Err` value: Syntax(UnclosedDoctype)
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

According to the XML specification, including < and > in an entity value literal is entirely legal. Merely checking the correspondence between < and > is insufficient to skip over the DTD.
In this sense, the current implementation's DTD handling is incorrect.