I'm a Java/Go/Python dev trying to get my feet wet with the C++ toolchain and having a hard time forcing CMake to find dependencies. I installed libxml++ on Debian using `apt-get install libxml++2.6-dev` and it installed it to `/usr/include/libxml++2.6/libxml++`. This is a problem, because that's not the right path relative to `/usr/include`--if I try to `#include <libxml++/libxml++.h>` it can't find it obviously, and if I include stuff as e.g. `#include <libxml++2.6/libxml++/whatever.h>` then `whatever.h` will be unable to find other header files searching for the `libxml++` path, e.g. `#include <libxml++/version.h>`. There are pkg-config files that come with the library but I couldn't really figure out what to do with them, and using stuff like `find_package(LibXml++)` or `include_directories(${LibXml++_INCLUDE_DIRS})` didn't work.

Looking at the CMake docs there appear to be several ways to solve every simple problem, and I feel like this must be a very simple problem with a simple solution if this is related to the way `apt-get` installs things. Is there something I can add to force CMake to look specifically in `/usr/include/[something]/libxml++` and still import it properly with relative paths, or do I need to just move stuff every time I install it with apt?

Apologies if this is a duplicate, but "libxml++" is an incredibly difficult library to Google, both because of the "++" punctuation and the fact that it's apparently not used anywhere near as much as regular libxml2. I'm happy to read more basic resources but would rather not slog through 30 years of the evolution of C++ to arrive at the answer.

For reference:

CMakeLists.txt:

```
cmake_minimum_required(VERSION 3.10)
project(sandbox)

set(CMAKE_CXX_STANDARD 17)

find_package(Boost REQUIRED)
find_package(LibXml2 REQUIRED)

include_directories(${CMAKE_CURRENT_SOURCE_DIR}/ ${LIBXML2_INCLUDE_DIR})
add_executable(sandbox main.cpp)
target_link_libraries(sandbox ${LIBXML2_LIBRARIES})

```

Source file:

```
#include <iostream>
#include <libxml++2.6/libxml++/libxml++.h>

int main() {
    std::cout << "hello" << std::endl;
}

```

Error msg:

```
[main] Building folder: cpp-sandbox 
[build] Starting build
[proc] Executing command: /usr/bin/cmake --build /workspaces/cpp-sandbox/build --config Debug --target all -- -j 6
[build] Scanning dependencies of target sandbox
[build] [ 50%] Building CXX object CMakeFiles/sandbox.dir/main.cpp.o
[build] In file included from /workspaces/cpp-sandbox/main.cpp:2:
[build] /usr/include/libxml++-2.6/libxml++/libxml++.h:50:10: fatal error: libxml++/exceptions/internal_error.h: No such file or directory
[build]  #include <libxml++/exceptions/internal_error.h>
[build]           ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
[build] compilation terminated.
[build] make[2]: *** [CMakeFiles/sandbox.dir/build.make:63: CMakeFiles/sandbox.dir/main.cpp.o] Error 1
[build] make[1]: *** [CMakeFiles/Makefile2:73: CMakeFiles/sandbox.dir/all] Error 2
[build] make: *** [Makefile:84: all] Error 2
[build] Build finished with exit code 2

```