CMake Targets & Properties
Modern CMake is targets all the way down: every include path, define, and flag is a property of a target, never a global leak.
Targets, not directories
Legacy CMake set global variables (include_directories, add_definitions) that leaked everywhere. Modern CMake attaches everything to targets:
add_library(fmtlib STATIC src/fmt.cpp)
target_include_directories(fmtlib PUBLIC include)
target_compile_features(fmtlib PUBLIC cxx_std_20)
target_compile_definitions(fmtlib PRIVATE FMTLIB_BUILDING)
The keyword is the contract: PUBLIC = needed by consumers too (propagates), PRIVATE = only while building me, INTERFACE = consumers only (header-only). A consumer that does target_link_libraries(app PRIVATE fmtlib) inherits exactly what it needs — usage requirements flow through the build graph.
Why this matters for correctness
Target scoping is not tidiness; it is correctness. A definition that leaks into a header you ship (because it was PUBLIC by accident) becomes an ODR hazard for every consumer that compiles with different flags (module 17). The build system is where binary compatibility begins.
Presets: reproducible configuration
CMakePresets.json pins generator, toolchain, and cache variables per configuration so cmake --preset release is the same on every machine — the entry point CI uses, and the reason "works on my machine" stops being a build bug.