$ pkg-config --debug libxslt
no output option set, defaulting to --exists
Error printing disabled by default due to use of output options --exists, --atleast/exact/max-version, --list-all or no output option at all. Value of --print-errors: 0
Error printing disabled
Adding virtual 'pkg-config' package to list of known packages
Looking for package 'libxslt'
Looking for package 'libxslt-uninstalled'
Reading 'libxslt' from file '/usr/local/Homebrew/Library/Homebrew/os/mac/pkgconfig/11.0/libxslt.pc'
Parsing package file '/usr/local/Homebrew/Library/Homebrew/os/mac/pkgconfig/11.0/libxslt.pc'
  line>homebrew_sdkroot=/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk
 Variable declaration, 'homebrew_sdkroot' has value '/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk'
  line>prefix=${homebrew_sdkroot}/usr
 Variable declaration, 'prefix' has value '/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr'
  line>exec_prefix=/usr
 Variable declaration, 'exec_prefix' has value '/usr'
  line>libdir=${exec_prefix}/lib
 Variable declaration, 'libdir' has value '/usr/lib'
  line>includedir=${prefix}/include
 Variable declaration, 'includedir' has value '/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include'
  line>
  line>
  line>Name: libxslt
  line>Version: 1.1.29
  line>Description: XSLT library version 2.
  line>Requires: libxml-2.0
  line>Libs: -L${libdir} -lxslt  -lxml2 -lz -lpthread -licucore -lm
  line>Cflags:
Path position of 'libxslt' is 4
Adding 'libxslt' to list of known packages
Searching for 'libxslt' requirement 'libxml-2.0'
Looking for package 'libxml-2.0'
Looking for package 'libxml-2.0-uninstalled'
Reading 'libxml-2.0' from file '/usr/local/Homebrew/Library/Homebrew/os/mac/pkgconfig/11.0/libxml-2.0.pc'
Parsing package file '/usr/local/Homebrew/Library/Homebrew/os/mac/pkgconfig/11.0/libxml-2.0.pc'
  line>homebrew_sdkroot=/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk
 Variable declaration, 'homebrew_sdkroot' has value '/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk'
  line>prefix=${homebrew_sdkroot}/usr
 Variable declaration, 'prefix' has value '/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr'
  line>exec_prefix=/usr
 Variable declaration, 'exec_prefix' has value '/usr'
  line>libdir=${exec_prefix}/lib
 Variable declaration, 'libdir' has value '/usr/lib'
  line>includedir=${prefix}/include
 Variable declaration, 'includedir' has value '/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include'
  line>modules=1
 Variable declaration, 'modules' has value '1'
  line>
  line>Name: libXML
  line>Version: 2.9.4
  line>Description: libXML library version2.
  line>Requires:
  line>Libs: -L${libdir} -lxml2
  line>Libs.private: -lz -lpthread -licucore -lm
Unknown keyword 'Libs.private' in '/usr/local/Homebrew/Library/Homebrew/os/mac/pkgconfig/11.0/libxml-2.0.pc'
  line>Cflags:
Path position of 'libxml-2.0' is 4
Adding 'libxml-2.0' to list of known packages
Package libxml-2.0 has -L /usr/lib in Libs
Removing -L /usr/lib from libs for libxml-2.0
Package libxslt has -L /usr/lib in Libs
Removing -L /usr/lib from libs for libxslt