RBT_HEAD.RBT_HEAD

Undocumented in source but is binding to C. You might be able to learn more by searching the web for its name.
template RBT_HEAD(string _name, string _type)
extern (C) nothrow @nogc
enum RBT_HEAD = "struct " ~ _name ~ " { libressl_d.compat.sys.tree.rb_tree rbh_root; }";

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