Why does abseil automatically add the namespace "absl::lts_2020_02_25"

Question

I built abseil with cmake, Finally I found out that abseil added a namespace "absl::lts 2020_02_25" which I didn't want, e.g.

0000000000020a2c T absl::lts_2020_02_25::StrAppend(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >*, absl::lts_2020_02_25::AlphaNum const&)

I use below cmd to build the abseil library

cd abseil-cpp
mkdir build && cd build
cmake -DBUILD_SHARED_LIBS=ON -DCMAKE_CXX_STANDARD=11 ..
cmake --build . --target all

nm absl/strings/libabsl_strings.so -C | grep StrAppend