diff --git a/eval.c b/eval.c
index ef98d7192e..a2cd523518 100644
--- a/eval.c
+++ b/eval.c
@@ -930,11 +930,6 @@ rb_jump_tag(int tag)
     EC_JUMP_TAG(GET_EC(), tag);
 }
 
-/*! Determines if the current method is given a block.
- * \retval zero if not given
- * \retval non-zero if given
- * \ingroup defmethod
- */
 int
 rb_block_given_p(void)
 {
@@ -956,11 +951,6 @@ rb_keyword_given_p(void)
 
 VALUE rb_eThreadError;
 
-/*! Declares that the current method needs a block.
- *
- * Raises a \c LocalJumpError if not given a block.
- * \ingroup defmethod
- */
 void
 rb_need_block(void)
 {
@@ -969,28 +959,6 @@ rb_need_block(void)
     }
 }
 
-/*! An equivalent of \c rescue clause.
- *
- * Equivalent to <code>begin .. rescue err_type .. end</code>
- *
- * \param[in] b_proc a function which potentially raises an exception.
- * \param[in] data1 the argument of \a b_proc
- * \param[in] r_proc a function which rescues an exception in \a b_proc.
- * \param[in] data2 the first argument of \a r_proc
- * \param[in] ... 1 or more exception classes. Must be terminated by \c (VALUE)0.
- *
- * First it calls the function \a b_proc, with \a data1 as the argument.
- * When \a b_proc raises an exception, it calls \a r_proc with \a data2 and
- * the exception object if the exception is a kind of one of the given
- * exception classes.
- *
- * \return the return value of \a b_proc if no exception occurs,
- *   or the return value of \a r_proc if otherwise.
- * \sa rb_rescue
- * \sa rb_ensure
- * \sa rb_protect
- * \ingroup exception
- */
 VALUE
 rb_rescue2(VALUE (* b_proc) (VALUE), VALUE data1,
            VALUE (* r_proc) (VALUE, VALUE), VALUE data2, ...)
@@ -1002,10 +970,6 @@ rb_rescue2(VALUE (* b_proc) (VALUE), VALUE data1,
     return ret;
 }
 
-/*!
- * \copydoc rb_rescue2
- * \param[in] args exception classes, terminated by (VALUE)0.
- */
 VALUE
 rb_vrescue2(VALUE (* b_proc) (VALUE), VALUE data1,
             VALUE (* r_proc) (VALUE, VALUE), VALUE data2,
@@ -1066,20 +1030,6 @@ rb_vrescue2(VALUE (* b_proc) (VALUE), VALUE data1,
     return result;
 }
 
-/*! An equivalent of \c rescue clause.
- *
- * Equivalent to <code>begin .. rescue .. end</code>.
- *
- * It is the same as
- * \code{cpp}
- * rb_rescue2(b_proc, data1, r_proc, data2, rb_eStandardError, (VALUE)0);
- * \endcode
- *
- * \sa rb_rescue2
- * \sa rb_ensure
- * \sa rb_protect
- * \ingroup exception
- */
 VALUE
 rb_rescue(VALUE (* b_proc)(VALUE), VALUE data1,
           VALUE (* r_proc)(VALUE, VALUE), VALUE data2)
@@ -1126,20 +1076,6 @@ rb_protect(VALUE (* proc) (VALUE), VALUE data, int *pstate)
     return result;
 }
 
-/*!
- * An equivalent to \c ensure clause.
- *
- * Equivalent to <code>begin .. ensure .. end</code>.
- *
- * Calls the function \a b_proc with \a data1 as the argument,
- * then calls \a e_proc with \a data2 when execution terminated.
- * \return The return value of \a b_proc if no exception occurred,
- *   or \c Qnil if otherwise.
- * \sa rb_rescue
- * \sa rb_rescue2
- * \sa rb_protect
- * \ingroup exception
- */
 VALUE
 rb_ensure(VALUE (*b_proc)(VALUE), VALUE data1, VALUE (*e_proc)(VALUE), VALUE data2)
 {
diff --git a/include/ruby/internal/iterator.h b/include/ruby/internal/iterator.h
index 70ac1bb94d..3512b0ac86 100644
--- a/include/ruby/internal/iterator.h
+++ b/include/ruby/internal/iterator.h
@@ -20,54 +20,488 @@
  *             extension libraries.  They could be written in C++98.
  * @brief      Block related APIs.
  */
+#include "ruby/internal/attr/deprecated.h"
 #include "ruby/internal/attr/noreturn.h"
 #include "ruby/internal/dllexport.h"
 #include "ruby/internal/value.h"
 
 RBIMPL_SYMBOL_EXPORT_BEGIN()
 
+/**
+ * @private
+ *
+ * @deprecated  This macro once was a thing in the old days, but makes no sense
+ *              any  longer today.   Exists  here  for backwards  compatibility
+ *              only.  You can safely forget about it.
+ */
 #define RB_BLOCK_CALL_FUNC_STRICT 1
+
+/**
+ * @private
+ *
+ * @deprecated  This macro once was a thing in the old days, but makes no sense
+ *              any  longer today.   Exists  here  for backwards  compatibility
+ *              only.  You can safely forget about it.
+ */
 #define RUBY_BLOCK_CALL_FUNC_TAKES_BLOCKARG 1
+
+/**
+ * Shim for block function parameters.  Historically ::rb_block_call_func_t had
+ * only two parameters.  Over time it evolved  to have much more than that.  By
+ * using this macro you can absorb such API differences.
+ *
+ * ```CXX
+ * // This works since 2.1.0
+ * VALUE my_own_iterator(RB_BLOCK_CALL_FUNC_ARGLIST(y, c));
+ * ```
+ */
 #define RB_BLOCK_CALL_FUNC_ARGLIST(yielded_arg, callback_arg) \
     VALUE yielded_arg, VALUE callback_arg, int argc, const VALUE *argv, VALUE blockarg
+
+/**
+ * This is the  type of a function that the  interpreter expect for C-backended
+ * blocks.  Blocks are  often written in Ruby.  But C  extensions might want to
+ * have their own blocks.  In order to  do so authors have to create a separate
+ * C function of this type, and pass its pointer to rb_block_call().
+ *
+ * ```CXX
+ * VALUE
+ * my_own_iterator(RB_BLOCK_CALL_FUNC_ARGLIST(y, c))
+ * {
+ *     const auto plus = rb_intern("+");
+ *     return rb_funcall(c, plus, 1, y);
+ * }
+ *
+ * VALUE
+ * my_own_method(VALUE self)
+ * {
+ *     const auto each = rb_intern("each");
+ *     return rb_block_call(self, each, 0, 0, my_own_iterator, self);
+ * }
+ * ```
+ */
 typedef VALUE rb_block_call_func(RB_BLOCK_CALL_FUNC_ARGLIST(yielded_arg, callback_arg));
+
+/**
+ * Shorthand type that represents an iterator-written-in-C function pointer.
+ */
 typedef rb_block_call_func *rb_block_call_func_t;
 
-VALUE rb_each(VALUE);
-VALUE rb_yield(VALUE);
+/**
+ * This is a shorthand of calling `obj.each`.
+ *
+ * @param[in]  obj  The receiver.
+ * @return     What `obj.each` returns.
+ *
+ * @internal
+ *
+ * Does anyone still need it?  This API  was to use with rb_iterate(), which is
+ * marked deprecated (see below).  Old idiom to call an iterator was:
+ *
+ * ```CXX
+ * VALUE recv;
+ * VALUE iter_func(ANYARGS);
+ * VALUE iter_data;
+ * rb_iterate(rb_each, recv, iter_func, iter_data);
+ * ```
+ */
+VALUE rb_each(VALUE obj);
+
+/**
+ * Yields the block.  In Ruby there is  a concept called a block.  You can pass
+ * one to a  method.  In a method, when  called with a block, you  can yield it
+ * using this function.
+ *
+ * ```CXX
+ * VALUE
+ * iterate(VALUE self)
+ * {
+ *     extern int get_n(VALUE);
+ *     extern VALUE get_v(VALUE, VALUE);
+ *     const auto n = get_n(self);
+ *
+ *     for (int i=0; i<n; i++) {
+ *         auto v = get_v(self, i);
+ *
+ *         rb_yield(v);
+ *     }
+ *     return self;
+ * }
+ * ```
+ *
+ * @param[in]  val                 Passed to the block.
+ * @exception  rb_eLocalJumpError  There is no block given.
+ * @return     Evaluated value of the given block.
+ */
+VALUE rb_yield(VALUE val);
+
+/**
+ * Identical to rb_yield(),  except it takes variadic number  of parameters and
+ * pass them to the block.
+ *
+ * @param[in]  n                   Number of parameters.
+ * @param[in]  ...                 List of arguments passed to the block.
+ * @exception  rb_eLocalJumpError  There is no block given.
+ * @return     Evaluated value of the given block.
+ */
 VALUE rb_yield_values(int n, ...);
+
+/**
+ * Identical to rb_yield_values(),  except it takes the parameters as a C array
+ * instead of variadic arguments.
+ *
+ * @param[in]  n                   Number of parameters.
+ * @param[in]  argv                List of arguments passed to the block.
+ * @exception  rb_eLocalJumpError  There is no block given.
+ * @return     Evaluated value of the given block.
+ */
 VALUE rb_yield_values2(int n, const VALUE *argv);
+
+/**
+ * Identical to  rb_yield_values2(), except you  can specify how to  handle the
+ * last element of the given array.
+ *
+ * @param[in]  n                   Number of parameters.
+ * @param[in]  argv                List of arguments passed to the block.
+ * @param[in]  kw_splat            Handling of keyword parameters:
+ *   - RB_NO_KEYWORDS              `ary`'s last is not a keyword argument.
+ *   - RB_PASS_KEYWORDS            `ary`'s last is a keyword argument.
+ *   - RB_PASS_CALLED_KEYWORDS     makes no sense here.
+ * @exception  rb_eLocalJumpError  There is no block given.
+ * @return     Evaluated value of the given block.
+ */
 VALUE rb_yield_values_kw(int n, const VALUE *argv, int kw_splat);
-VALUE rb_yield_splat(VALUE);
-VALUE rb_yield_splat_kw(VALUE, int);
+
+/**
+ * Identical to  rb_yield_values(), except it  splats an array to  generate the
+ * list of parameters.
+ *
+ * @param[in]  ary                 Array to splat.
+ * @exception  rb_eLocalJumpError  There is no block given.
+ * @return     Evaluated value of the given block.
+ */
+VALUE rb_yield_splat(VALUE ary);
+
+/**
+ * Identical to rb_yield_splat(), except you can specify how to handle the last
+ * element of the given array.
+ *
+ * @param[in]  ary                 Array to splat.
+ * @param[in]  kw_splat            Handling of keyword parameters:
+ *   - RB_NO_KEYWORDS              `ary`'s last is not a keyword argument.
+ *   - RB_PASS_KEYWORDS            `ary`'s last is a keyword argument.
+ *   - RB_PASS_CALLED_KEYWORDS     makes no sense here.
+ * @exception  rb_eLocalJumpError  There is no block given.
+ * @return     Evaluated value of the given block.
+ */
+VALUE rb_yield_splat_kw(VALUE ary, int kw_splat);
+
+/**
+ * Pass a passed block.
+ *
+ * Sometimes you  want to "pass" a  block form one method  to another.  Suppose
+ * you have this Ruby method `foo`:
+ *
+ * ```ruby
+ * def foo(x, y)
+ *   x.open(y) do |*z|
+ *     yield(*z)
+ *   end
+ * end
+ * ```
+ *
+ * And  suppose you  want  to  translate this  into  C.  Then  rb_yield_block()
+ * function is usable in this situation.
+ *
+ * ```CXX
+ * VALUE
+ * foo_translated_into_C(VALUE self, VALUE x, VALUE y)
+ * {
+ *     const auto open = rb_intern("open");
+ *
+ *     return rb_block_call(x, open, 1, &y, rb_yield_block, Qfalse);
+ *     //                                   ^^^^^^^^^^^^^^  Here.
+ * }
+ * ```
+ *
+ * @see rb_funcall_passing_block
+ *
+ * @internal
+ *
+ * @shyouhei  honestly  doesn't understand  why  this  is needed,  given  there
+ * already was rb_funcall_passing_block()  at the time it  was implemented.  If
+ * somebody knows its raison d'etre, please improve the document :FIXME:
+ */
 VALUE rb_yield_block(RB_BLOCK_CALL_FUNC_ARGLIST(yielded_arg, callback_arg)); /* rb_block_call_func */
+
+/**
+ * Determines if the current method is given a keyword argument.
+ *
+ * @retval  false  No keyword argument is given.
+ * @retval  true   Keyword argument(s) are given.
+ * @ingroup defmethod
+ */
 int rb_keyword_given_p(void);
+
+/**
+ * Determines if the current method is given a block.
+ *
+ * @retval  false  No block is given.
+ * @retval  true   A block is given.
+ * @ingroup defmethod
+ *
+ * @internal
+ *
+ * This function should have returned a bool.   But at the time it was designed
+ * the project was entirely written in K&R C.
+ */
 int rb_block_given_p(void);
+
+/**
+ * Declares that the current method needs a block.
+ *
+ * @exception  rb_eLocalJumpError  No block given.
+ * @ingroup    defmethod
+ */
 void rb_need_block(void);
-VALUE rb_iterate(VALUE(*)(VALUE),VALUE,rb_block_call_func_t,VALUE);
+
+RBIMPL_ATTR_DEPRECATED(("by: rb_block_call since 1.9"))
+/**
+ * Old way to iterate a block.
+ *
+ * @deprecated     This is an old API.  Use rb_block_call() instead.
+ * @warning        The passed  function must at  least once call a  ruby method
+ *                 (to handle interrupts etc.)
+ * @param[in]      func1  A function that could yield a value.
+ * @param[in,out]  data1  Passed to `func1`
+ * @param[in]      proc   A function acts as a block.
+ * @param[in,out]  data2  Passed to `proc` as the data2 parameter.
+ * @return         What `func1` returns.
+ */
+VALUE rb_iterate(VALUE (*func1)(VALUE), VALUE data1, rb_block_call_func_t proc, VALUE data2);
+
 #ifdef __cplusplus
-namespace ruby {namespace backward {
+namespace ruby {
+namespace backward {
+/**
+ * Old way to iterate a block.
+ *
+ * @deprecated     This is an old API.  Use rb_block_call() instead.
+ * @warning        The passed  function must at  least once call a  ruby method
+ *                 (to handle interrupts etc.)
+ * @param[in]      iter   A function that could yield a value.
+ * @param[in,out]  data1  Passed to `func1`
+ * @param[in]      bl     A function acts as a block.
+ * @param[in,out]  data2  Passed to `proc` as the data2 parameter.
+ * @return         What `func1` returns.
+ */
 static inline VALUE
 rb_iterate_deprecated(VALUE (*iter)(VALUE), VALUE data1, rb_block_call_func_t bl, VALUE data2)
 {
     return ::rb_iterate(iter, data1, bl, data2);
 }}}
 #endif
-DEPRECATED_BY(rb_block_call since 1.9, VALUE rb_iterate(VALUE(*)(VALUE),VALUE,rb_block_call_func_t,VALUE));
-VALUE rb_block_call(VALUE,ID,int,const VALUE*,rb_block_call_func_t,VALUE);
-VALUE rb_block_call_kw(VALUE,ID,int,const VALUE*,rb_block_call_func_t,VALUE,int);
-VALUE rb_rescue(VALUE(*)(VALUE),VALUE,VALUE(*)(VALUE,VALUE),VALUE);
-VALUE rb_rescue2(VALUE(*)(VALUE),VALUE,VALUE(*)(VALUE,VALUE),VALUE,...);
-VALUE rb_vrescue2(VALUE(*)(VALUE),VALUE,VALUE(*)(VALUE,VALUE),VALUE,va_list);
-VALUE rb_ensure(VALUE(*)(VALUE),VALUE,VALUE(*)(VALUE),VALUE);
-VALUE rb_catch(const char*,rb_block_call_func_t,VALUE);
-VALUE rb_catch_obj(VALUE,rb_block_call_func_t,VALUE);
+
+/**
+ * Identical to  rb_funcallv(), except it  additionally passes a function  as a
+ * block.  When the  method yields, `proc` is called with  the yielded value as
+ * its first  argument, and  `data2` as  the second.   Yielded values  would be
+ * packed into an array if multiple values are yielded at once.
+ *
+ * @param[in,out]  obj    Receiver.
+ * @param[in]      mid    Method signature.
+ * @param[in]      argc   Number of arguments.
+ * @param[in]      argv   Arguments passed to `obj.mid`.
+ * @param[in]      proc   A function acts as a block.
+ * @param[in,out]  data2  Passed to `proc` as the data2 parameter.
+ * @return         What `obj.mid` returns.
+ */
+VALUE rb_block_call(VALUE obj, ID mid, int argc, const VALUE *argv, rb_block_call_func_t proc, VALUE data2);
+
+/**
+ * Identical to rb_funcallv_kw(), except it additionally passes a function as a
+ * block.   It can  also be  seen as  a routine  identical to  rb_block_call(),
+ * except it handles keyword-ness of `argv[argc-1]`.
+ *
+ * @param[in,out]  obj       Receiver.
+ * @param[in]      mid       Method signature.
+ * @param[in]      argc      Number of arguments including the keywords.
+ * @param[in]      argv      Arguments passed to `obj.mid`.
+ * @param[in]      proc      A function acts as a block.
+ * @param[in,out]  data2     Passed to `proc` as the data2 parameter.
+ * @param[in]      kw_splat  Handling of keyword parameters:
+ *   - RB_NO_KEYWORDS           `argv`'s last is not a keyword argument.
+ *   - RB_PASS_KEYWORDS         `argv`'s last is a keyword argument.
+ *   - RB_PASS_CALLED_KEYWORDS  it depends if there is a passed block.
+ * @return         What `obj.mid` returns.
+ */
+VALUE rb_block_call_kw(VALUE obj, ID mid, int argc, const VALUE *argv, rb_block_call_func_t proc, VALUE data2, int kw_splat);
+
+/**
+ * Identical  to rb_rescue2(),  except it  does not  take a  list of  exception
+ * classes.  This is a shorthand of:
+ *
+ * ```CXX
+ * rb_rescue2(b_proc, data1, r_proc, data2, rb_eStandardError, (VALUE)0);
+ * ```
+ *
+ * @param[in]      b_proc  A function which potentially raises an exception.
+ * @param[in,out]  data1   Passed to `b_proc`.
+ * @param[in]      r_proc  A function which rescues an exception in `b_proc`.
+ * @param[in,out]  data2   The first argument of `r_proc`.
+ * @return         The return value of `b_proc`  if no exception occurs, or the
+ *                 return value of `r_proc` otherwise.
+ * @see            rb_rescue
+ * @see            rb_ensure
+ * @see            rb_protect
+ * @ingroup        exception
+ */
+VALUE rb_rescue(VALUE (*b_proc)(VALUE), VALUE data1, VALUE (*r_proc)(VALUE, VALUE), VALUE data2);
+
+/**
+ * An equivalent of `rescue` clause.
+ *
+ * First  it calls  the function  `b_proc` with  `data1` as  the argument.   If
+ * nothing is thrown the function happily returns the return value of `b_proc`.
+ * When `b_proc` raises an exception, and the exception is a kind of one of the
+ * given  exception classes,  it  then  calls `r_proc`  with  `data2` and  that
+ * exception.  If the exception does not match any of them, it propagates.
+ *
+ * @param[in]      b_proc  A function which potentially raises an exception.
+ * @param[in,out]  data1   Passed to `b_proc`.
+ * @param[in]      r_proc  A function which rescues an exception in `b_proc`.
+ * @param[in,out]  data2   The first argument of `r_proc`.
+ * @param[in]      ...     1 or  more exception classes.  Must be terminated by
+ *                         `(VALUE)0`
+ * @return         The return value of `b_proc`  if no exception occurs, or the
+ *                 return value of `r_proc` otherwise.
+ * @see            rb_rescue
+ * @see            rb_ensure
+ * @see            rb_protect
+ * @ingroup        exception
+ */
+VALUE rb_rescue2(VALUE (*b_proc)(VALUE), VALUE data1, VALUE (*r_proc)(VALUE, VALUE), VALUE data2, ...);
+
+/**
+ * Identical to  rb_rescue2(), except  it takes  `va_list` instead  of variadic
+ * number  of  arguments.   This  is  exposed to  3rd  parties  because  inline
+ * functions use it.  Basically you don't have to bother.
+ *
+ * @param[in]      b_proc  A function which potentially raises an exception.
+ * @param[in,out]  data1   Passed to `b_proc`.
+ * @param[in]      r_proc  A function which rescues an exception in `b_proc`.
+ * @param[in,out]  data2   The first argument of `r_proc`.
+ * @param[in]      ap      1 or  more exception classes.  Must be terminated by
+ *                         `(VALUE)0`
+ * @return         The return value of `b_proc`  if no exception occurs, or the
+ *                 return value of `r_proc` otherwise.
+ * @see            rb_rescue
+ * @see            rb_ensure
+ * @see            rb_protect
+ * @ingroup        exception
+ */
+VALUE rb_vrescue2(VALUE (*b_proc)(VALUE), VALUE data1, VALUE (*r_proc)(VALUE, VALUE), VALUE data2, va_list ap);
+
+/**
+ * An equivalent to `ensure` clause.   Calls the function `b_proc` with `data1`
+ * as the argument, then calls `e_proc` with `data2` when execution terminated.
+ *
+ * @param[in]      b_proc     A function representing begin clause.
+ * @param[in,out]  data1      Passed to `b_proc`.
+ * @param[in]      e_proc     A function representing ensure clause.
+ * @param[in,out]  data2      Passed to `e_proc`.
+ * @retval         RUBY_Qnil  exception occurred inside of `b_proc`.
+ * @retval         otherwise  The return value of `b_proc`.
+ * @see            rb_rescue
+ * @see            rb_rescue2
+ * @see            rb_protect
+ * @ingroup        exception
+ */
+VALUE rb_ensure(VALUE (*b_proc)(VALUE), VALUE data1, VALUE (*e_proc)(VALUE), VALUE data2);
+
+/**
+ * Executes the passed block and catches values thrown from inside of it.
+ *
+ * In case  the block does  not contain any  throw`, this function  returns the
+ * value of the last expression evaluated.
+ *
+ * ```CXX
+ * VALUE
+ * iter(RB_BLOCK_CALL_FUNC_ARGLIST(yielded, callback))
+ * {
+ *     return INT2FIX(123);
+ * }
+ *
+ * VALUE
+ * method(VALUE self)
+ * {
+ *     return rb_catch("tag", iter, Qnil); // returns 123
+ * }
+ * ```
+ *
+ * In case there do exist `throw`, Ruby searches up its execution context for a
+ * `catch` block.   When a matching catch  is found, the block  stops executing
+ * and returns that thrown value instead.
+ *
+ * ```CXX
+ * VALUE
+ * iter(RB_BLOCK_CALL_FUNC_ARGLIST(yielded, callback))
+ * {
+ *     rb_throw("tag", 456);
+ *     return INT2FIX(123);
+ * }
+ *
+ * VALUE
+ * method(VALUE self)
+ * {
+ *     return rb_catch("tag", iter, Qnil); // returns 456
+ * }
+ * ```
+ *
+ * @param[in]      tag   Arbitrary tag string.
+ * @param[in]      func  Function pointer that acts as a block.
+ * @param[in,out]  data  Extra parameter passed to `func`.
+ * @return         Either caught value for `tag`, or the return value of `func`
+ *                 if nothing is thrown.
+ */
+VALUE rb_catch(const char *tag, rb_block_call_func_t func, VALUE data);
+
+/**
+ * Identical to rb_catch(), except it catches arbitrary Ruby objects.
+ *
+ * @param[in]      tag   Arbitrary tag object.
+ * @param[in]      func  Function pointer that acts as a block.
+ * @param[in,out]  data  Extra parameter passed to `func`.
+ * @return         Either caught value for `tag`, or the return value of `func`
+ *                 if nothing is thrown.
+ */
+VALUE rb_catch_obj(VALUE tag, rb_block_call_func_t func, VALUE data);
 
 RBIMPL_ATTR_NORETURN()
-void rb_throw(const char*,VALUE);
+/**
+ * Transfers control to the end of  the active `catch` block waiting for `tag`.
+ * Raises  rb_eUncughtThrow if  there is  no `catch`  block for  the tag.   The
+ * second  parameter supplies  a  return  value for  the  `catch` block,  which
+ * otherwise defaults to ::RUBY_Qnil.  For examples, see rb_catch().
+ *
+ * @param[in]  tag               Tag string.
+ * @param[in]  val               Value to throw.
+ * @exception  rb_eUncughtThrow  There is no corresponding `catch` clause.
+ * @note       It never returns.
+ */
+void rb_throw(const char *tag, VALUE val);
 
 RBIMPL_ATTR_NORETURN()
-void rb_throw_obj(VALUE,VALUE);
+/**
+ * Identical to rb_throw(), except it allows  arbitrary Ruby object to become a
+ * tag.
+ *
+ * @param[in]  tag               Arbitrary object.
+ * @param[in]  val               Value to throw.
+ * @exception  rb_eUncughtThrow  There is no corresponding `catch` clause.
+ * @note       It never returns.
+ */
+void rb_throw_obj(VALUE tag, VALUE val);
 
 RBIMPL_SYMBOL_EXPORT_END()