diff --git a/ext/stringio/stringio.c b/ext/stringio/stringio.c
index ca71bb48..9a863b6b 100644
--- a/ext/stringio/stringio.c
+++ b/ext/stringio/stringio.c
@@ -1428,15 +1428,177 @@ strio_readline(int argc, VALUE *argv, VALUE self)
 }
 
 /*
+ * :markup: markdown
+ *
  * call-seq:
  *   each_line(sep = $/, chomp: false) {|line| ... }   -> self
  *   each_line(limit, chomp: false) {|line| ... }      -> self
  *   each_line(sep, limit, chomp: false) {|line| ... } -> self
  *
- * Calls the block with each remaining line read from the stream;
- * does nothing if already at end-of-file;
- * returns +self+.
- * See {Line IO}[rdoc-ref:IO@Line+IO].
+ * With a block given calls the block with each remaining line (see "Position" below) in the stream;
+ * returns `self`.
+ *
+ * Leaves stream position as end-of-stream.
+ *
+ * **No Arguments**
+ *
+ * With no arguments given,
+ * reads lines using the default record separator global variable `$/`, whose initial value is `"\n"`.
+ *
+ * ```
+ * strio = StringIO.new(TEXT)
+ * strio.each_line {|line| p line }
+ * strio.eof? # => true
+ * ```
+ *
+ * Output:
+ *
+ * ```
+ * "First line\n"
+ * "Second line\n"
+ * "\n"
+ * "Fourth line\n"
+ * "Fifth line\n"
+ * ```
+ *
+ * **Argument `sep`**
+ *
+ * With only string argument `sep` given,
+ * reads lines using that string as the record separator:
+ *
+ * ```
+ * strio = StringIO.new(TEXT)
+ * strio.each_line(' ') {|line| p line }
+ * ```
+ *
+ * Output:
+ *
+ * ```
+ * "First "
+ * "line\nSecond "
+ * "line\n\nFourth "
+ * "line\nFifth "
+ * "line\n"
+ * ```
+ *
+ * **Argument `limit`**
+ *
+ * With only integer argument `limit` given,
+ * reads lines using the default record separator global variable `$/`, whose initial value is `"\n"`;
+ * also limits the size (in characters) of each line to the given limit:
+ *
+ * ```
+ * strio = StringIO.new(TEXT)
+ * strio.each_line(10) {|line| p line }
+ * ```
+ *
+ * Output:
+ *
+ * ```
+ * "First line"
+ * "\n"
+ * "Second lin"
+ * "e\n"
+ * "\n"
+ * "Fourth lin"
+ * "e\n"
+ * "Fifth line"
+ * "\n"
+ * ```
+ * **Arguments `sep` and `limit`**
+ *
+ * With arguments `sep` and `limit` both given,
+ * honors both:
+ *
+ * ```
+ * strio = StringIO.new(TEXT)
+ * strio.each_line(' ', 10) {|line| p line }
+ * ```
+ *
+ * Output:
+ *
+ * ```
+ * "First "
+ * "line\nSecon"
+ * "d "
+ * "line\n\nFour"
+ * "th "
+ * "line\nFifth"
+ * " "
+ * "line\n"
+ * ```
+ *
+ * **Position**
+ *
+ * As stated above, method `each` _remaining_ line in the stream.
+ *
+ * In the examples above each `strio` object starts with its position at beginning-of-stream;
+ * but in other cases the position may be anywhere (see StringIO#pos):
+ *
+ * ```
+ * strio = StringIO.new(TEXT)
+ * strio.pos = 30 # Set stream position to character 30.
+ * strio.each_line {|line| p line }
+ * ```
+ *
+ * Output:
+ *
+ * ```
+ * " line\n"
+ * "Fifth line\n"
+ * ```
+ *
+ * **Special Record Separators**
+ *
+ * Like some methds in class `IO`, StringIO.each honors two special record separators;
+ * see {Special Line Separators}[https://docs.ruby-lang.org/en/master/IO.html#class-IO-label-Special+Line+Separator+Values].
+ *
+ * ```
+ * strio = StringIO.new(TEXT)
+ * strio.each_line('') {|line| p line } # Read as paragraphs (separated by blank lines).
+ * ```
+ *
+ * Output:
+ *
+ * ```
+ * "First line\nSecond line\n\n"
+ * "Fourth line\nFifth line\n"
+ * ```
+ *
+ * ```
+ * strio = StringIO.new(TEXT)
+ * strio.each_line(nil) {|line| p line } # "Slurp"; read it all.
+ * ```
+ *
+ * Output:
+ *
+ * ```
+ * "First line\nSecond line\n\nFourth line\nFifth line\n"
+ * ```
+ *
+ * **Keyword Argument `chomp`**
+ *
+ * With keyword argument `chomp` given as `true` (the default is `false`),
+ * removes trailing newline (if any) from each line:
+ *
+ * ```
+ * strio = StringIO.new(TEXT)
+ * strio.each_line(chomp: true) {|line| p line }
+ * ```
+ *
+ * Output:
+ *
+ * ```
+ * "First line"
+ * "Second line"
+ * ""
+ * "Fourth line"
+ * "Fifth line"
+ * ```
+ *
+ * With no block given, returns a new  {Enumerator}[https://docs.ruby-lang.org/en/master/Enumerator.html].
+ *
+ * Related: StringIO.each_byte, StringIO.each_char, StringIO.each_codepoint.
  */
 static VALUE
 strio_each(int argc, VALUE *argv, VALUE self)
@@ -1935,15 +2097,34 @@ strio_set_encoding_by_bom(VALUE self)
 }
 
 /*
+ * :markup: markdown
+ *
  * \IO streams for strings, with access similar to
  * {IO}[rdoc-ref:IO];
  * see {IO}[rdoc-ref:IO].
  *
- * === About the Examples
+ * ### About the Examples
  *
  * Examples on this page assume that \StringIO has been required:
  *
- *   require 'stringio'
+ * ```
+ * require 'stringio'
+ * ```
+ *
+ * And that these constants have been defined:
+ *
+ * ```
+ * TEXT = <<EOT
+ * First line
+ * Second line
+ *
+ * Fourth line
+ * Fifth line
+ * EOT
+ *
+ * RUSSIAN = 'тест'
+ * DATA = "\u9990\u9991\u9992\u9993\u9994"
+ * ```
  *
  */
 void