No package ‘libxml-2.0’ found

在configure过程还可能出现一个问题：

checking for LIBXML2... configure: error: Package requirements (libxml-2.0 >= 2.6) were not met:
No package 'libxml-2.0' found
Consider adjusting the PKG_CONFIG_PATH environment variable if you

installed software in a non-standard prefix.
Alternatively, you may set the environment variables LIBXML2_CFLAGS

and LIBXML2_LIBS to avoid the need to call pkg-config.

See the pkg-config man page for more details.
应该是XML库指定路径错误，重新指定：
./configure  --prefix=ParseError: KaTeX parse error: Undefined control sequence: \
 at position 38: …ips-linux-gnu  \̲
̲LIBXML2_LIBS='-…{xml_install_dir}/lib -lxml2' LIBXML2_CFLAGS='-I${xml_install_dir}/include/libxml2'

还是不行，debug了很久，最后发现打开configure文件发现：
if test -n "$libxml2_LIBS"; then
    pkg_cv_libxml2_LIBS="$libxml2_LIBS"

难道要小写？
./configure  --prefix=ParseError: KaTeX parse error: Undefined control sequence: \
 at position 38: …ips-linux-gnu  \̲
̲libxml2_LIBS='-…{xml_install_dir}/lib -lxml2' libxml2_CFLAGS='-I${xml_install_dir}/include/libxml2'

改成小写果然可以了，真是防不胜防啊