Install expat with Homebrew

Project links

• Homepage
• Repository

Commands and aliases

• xmlwf

Project history

The official repository describes Expat as a C99 library for parsing XML 1.0, started by James Clark in 1997. Its model is event-oriented: users register handlers before parsing, and those handlers are called as document structures are discovered.

The project site frames Expat around streaming rather than building a full in-memory document tree. That makes it useful for files too large to fit in memory, and for applications where parser performance and flexible callbacks are more important than a high-level DOM interface.

Adoption history

The Expat homepage states that numerous applications, libraries, and hardware use Expat, that bindings and third-party wrappers exist, and that Expat is packaged everywhere. That breadth is the key adoption story: many users never invoke xmlwf directly, but they depend on Expat through another program or language runtime.

The repository README documents common build-system integration, including CMake find_package usage. That is a sign of mature library adoption: Expat is not just an executable in package managers, but a dependency with headers, link targets, and ABI expectations.

How it is used

Developers use libexpat when they want a C XML parser that calls application-defined handlers for starts, ends, character data, and related XML structures. The included xmlwf executable is used to check whether XML input is well formed.

Because XML parsers sit at input boundaries, Expat's package history is often security-driven. The official GitHub issue tracker includes release coordination that references downstream updates in CPython, Gentoo, Spack, Homebrew, NixOS, MSYS2, and other packaging ecosystems when CVE fixes land.

Why package nerds care

Expat is a dependency-package archetype: boring when healthy, urgent when vulnerable. It is small enough to be embedded or vendored, but important enough that a security update can ripple through Python, Linux distributions, language package sets, and embedded builds.

The package also demonstrates the difference between library identity and command identity. Homebrew exposes xmlwf as the executable, while the real package value is libexpat and its headers.

Timeline

• 1997: James Clark started Expat.
• 2.4.x: Security releases triggered broad downstream package updates.
• 2025: Expat 2.7.2 release coordination referenced Homebrew, CPython, NixOS, MSYS2, Spack, Gentoo, and other downstreams.
• 2026: Expat 2.8.x release coordination continued around security fixes and downstream updates.

Related projects

• CPython is a major downstream because Python includes pyexpat bindings and coordinates bundled Expat updates.
• CMake's FindEXPAT module is an important integration path for C and C++ projects.
• Other XML parsers are related by role, but Expat's official documentation emphasizes its streaming C API.

Sources

• https://github.com/libexpat/libexpat
• https://libexpat.github.io/
• https://libexpat.github.io/doc/
• https://libexpat.github.io/doc/api/latest/
• https://github.com/libexpat/libexpat/issues/1030
• https://github.com/libexpat/libexpat/issues/1214