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+Returns a new \String object containing the given +string+.
+
+The +options+ are optional keyword options (see below).
+
+With no argument given and keyword +encoding+ also not given,
+returns an empty string with the Encoding <tt>ASCII-8BIT</tt>:
+
+  s = String.new # => ""
+  s.encoding     # => #<Encoding:ASCII-8BIT>
+
+With argument +string+ given and keyword option +encoding+ not given,
+returns a new string with the same encoding as +string+:
+
+  s0 = 'foo'.encode(Encoding::UTF_16)
+  s1 = String.new(s0)
+  s1.encoding # => #<Encoding:UTF-16 (dummy)>
+
+(Unlike \String.new,
+a {string literal}[rdoc-ref:syntax/literals.rdoc@String+Literals] like <tt>''</tt> or a
+{here document literal}[rdoc-ref:syntax/literals.rdoc@Here+Document+Literals]
+always has {script encoding}[rdoc-ref:encodings.rdoc@Script+Encoding].)
+
+With keyword option +encoding+ given,
+returns a string with the specified encoding;
+the +encoding+ may be an Encoding object, an encoding name,
+or an encoding name alias:
+
+  String.new(encoding: Encoding::US_ASCII).encoding        # => #<Encoding:US-ASCII>
+  String.new('', encoding: Encoding::US_ASCII).encoding    # => #<Encoding:US-ASCII>
+  String.new('foo', encoding: Encoding::US_ASCII).encoding # => #<Encoding:US-ASCII>
+  String.new('foo', encoding: 'US-ASCII').encoding         # => #<Encoding:US-ASCII>
+  String.new('foo', encoding: 'ASCII').encoding            # => #<Encoding:US-ASCII>
+
+The given encoding need not be valid for the string's content,
+and its validity is not checked:
+
+  s = String.new('こんにちは', encoding: 'ascii')
+  s.valid_encoding? # => false
+
+But the given +encoding+ itself is checked:
+
+  String.new('foo', encoding: 'bar') # Raises ArgumentError.
+
+With keyword option +capacity+ given,
+the given value is advisory only,
+and may or may not set the size of the internal buffer,
+which may in turn affect performance:
+
+  String.new('foo', capacity: 1)    # Buffer size is at least 4 (includes terminal null byte).
+  String.new('foo', capacity: 4096) # Buffer size is at least 4;
+                                    # may be equal to, greater than, or less than 4096.