Add "Example" label to example code blocks

The label should help users distinguish example code blocks from other
code blocks, such as method source code.

It's only applied to Ruby code examples.

Author: st0012

lib/rdoc/generator/template/darkfish/css/rdoc.css

@@ -597,6 +597,24 @@ main .method-source-code.active-menu {
   max-height: 100vh;
 }
 
+main .method-example::before {
+  content: "Example";
+  color: var(--secondary-color);
+  border-bottom: 1px solid var(--border-color);
+  display: block;
+  padding: 10px 0;
+  font-size: 0.9em;
+  margin-bottom: 10px;
+}
+
+main .method-example {
+  margin: 0;
+  padding: 0px 16px 16px 16px;
+  overflow-x: auto;
+  border-radius: 4px;
+  border-color: var(--border-color);
+}
+
 main .method-description .method-calls-super {
   color: var(--text-color);
   font-weight: bold;

lib/rdoc/markup/to_html.rb

@@ -221,7 +221,7 @@ def accept_verbatim verbatim
     content = if verbatim.ruby? or parseable? text then
                 begin
                   tokens = RDoc::Parser::RipperStateLex.parse text
-                  klass  = ' class="ruby"'
+                  klass  = ' class="ruby method-example"'
 
                   result = RDoc::TokenStream.to_html tokens
                   result = result + "\n" unless "\n" == result[-1]

test/rdoc/test_rdoc_markup_to_html.rb

@@ -293,7 +293,7 @@ def accept_rule
   end
 
   def accept_verbatim
-    assert_equal "\n<pre class=\"ruby\"><span class=\"ruby-identifier\">hi</span>\n  <span class=\"ruby-identifier\">world</span>\n</pre>\n", @to.res.join
+    assert_equal "\n<pre class=\"ruby method-example\"><span class=\"ruby-identifier\">hi</span>\n  <span class=\"ruby-identifier\">world</span>\n</pre>\n", @to.res.join
   end
 
   def end_accepting
@@ -459,7 +459,7 @@ def test_accept_verbatim_parseable
 
     expected = <<-EXPECTED
 
-<pre class="ruby"><span class="ruby-keyword">class</span> <span class="ruby-constant">C</span>
+<pre class="ruby method-example"><span class="ruby-keyword">class</span> <span class="ruby-constant">C</span>
 <span class="ruby-keyword">end</span>
 </pre>
     EXPECTED
@@ -491,7 +491,7 @@ def test_accept_verbatim_nl_after_backslash
 
     expected = <<-EXPECTED
 
-<pre class="ruby"><span class="ruby-identifier">a</span> = <span class="ruby-value">1</span> <span class="ruby-keyword">if</span> <span class="ruby-identifier">first_flag_var</span> <span class="ruby-keyword">and</span> \\
+<pre class="ruby method-example"><span class="ruby-identifier">a</span> = <span class="ruby-value">1</span> <span class="ruby-keyword">if</span> <span class="ruby-identifier">first_flag_var</span> <span class="ruby-keyword">and</span> \\
   <span class="ruby-identifier">this_is_flag_var</span>
 </pre>
     EXPECTED
@@ -549,7 +549,7 @@ def bar
 
     expected = <<-'EXPECTED'
 
-<pre class="ruby"><span class="ruby-keyword">def</span> <span class="ruby-identifier ruby-title">foo</span>
+<pre class="ruby method-example"><span class="ruby-keyword">def</span> <span class="ruby-identifier ruby-title">foo</span>
   [
     <span class="ruby-string">&#39;\\&#39;</span>,
     <span class="ruby-string">&#39;\&#39;&#39;</span>,
@@ -599,7 +599,7 @@ def bar
 
     expected = <<-'EXPECTED'
 
-<pre class="ruby"><span class="ruby-keyword">def</span> <span class="ruby-identifier ruby-title">foo</span>
+<pre class="ruby method-example"><span class="ruby-keyword">def</span> <span class="ruby-identifier ruby-title">foo</span>
   [
     <span class="ruby-string">`\\`</span>,
     <span class="ruby-string">`\&#39;\&quot;\``</span>,
@@ -626,7 +626,7 @@ def test_accept_verbatim_ruby
 
     expected = <<-EXPECTED
 
-<pre class="ruby"><span class="ruby-value">1</span> <span class="ruby-operator">+</span> <span class="ruby-value">1</span>
+<pre class="ruby method-example"><span class="ruby-value">1</span> <span class="ruby-operator">+</span> <span class="ruby-value">1</span>
 </pre>
     EXPECTED
 
@@ -645,7 +645,7 @@ def test_accept_verbatim_redefinable_operators
 
     expected = <<-EXPECTED
 
-<pre class="ruby">
+<pre class="ruby method-example">
     EXPECTED
     expected = expected.rstrip
 
@@ -880,8 +880,8 @@ def test_list_verbatim_2
 <ul><li>
 <p>one</p>
 
-<pre class=\"ruby\"><span class=\"ruby-identifier\">verb1</span>
-<span class=\"ruby-identifier\">verb2</span>
+<pre class="ruby method-example"><span class="ruby-identifier">verb1</span>
+<span class="ruby-identifier">verb2</span>
 </pre>
 </li><li>
 <p>two</p>

test/rdoc/test_rdoc_markup_to_html_snippet.rb

@@ -310,7 +310,7 @@ def accept_rule
   end
 
   def accept_verbatim
-    assert_equal "\n<pre class=\"ruby\"><span class=\"ruby-identifier\">hi</span>\n  <span class=\"ruby-identifier\">world</span>\n</pre>\n", @to.res.join
+    assert_equal "\n<pre class=\"ruby method-example\"><span class=\"ruby-identifier\">hi</span>\n  <span class=\"ruby-identifier\">world</span>\n</pre>\n", @to.res.join
     assert_equal 10, @to.characters
   end
 
@@ -404,7 +404,7 @@ def test_accept_verbatim_ruby
 
     expected = <<-EXPECTED
 
-<pre class="ruby"><span class="ruby-keyword">class</span> <span class="ruby-constant">C</span>
+<pre class="ruby method-example"><span class="ruby-keyword">class</span> <span class="ruby-constant">C</span>
 <span class="ruby-keyword">end</span>
 </pre>
     EXPECTED
@@ -586,8 +586,8 @@ def test_convert_limit_verbatim_multiline
     expected = <<-EXPECTED
 <p>Look for directives in a normal comment block:
 
-<pre class=\"ruby\"><span class=\"ruby-comment\"># :stopdoc:</span>
-<span class=\"ruby-comment\">#{inner}</span>
+<pre class="ruby method-example"><span class="ruby-comment"># :stopdoc:</span>
+<span class="ruby-comment">#{inner}</span>
 </pre>
     EXPECTED
 
@@ -664,8 +664,8 @@ def test_list_verbatim_2
     expected = <<-EXPECTED
 <p>one
 
-<pre class=\"ruby\"><span class=\"ruby-identifier\">verb1</span>
-<span class=\"ruby-identifier\">verb2</span>
+<pre class="ruby method-example"><span class="ruby-identifier">verb1</span>
+<span class="ruby-identifier">verb2</span>
 </pre>
 <p>two
 

test/rdoc/test_rdoc_parser_ruby.rb

@@ -2984,7 +2984,7 @@ def blah
     expected = <<EXPECTED
 <p>doc
 
-<pre class="ruby"><span class="ruby-comment">=begin
+<pre class="ruby method-example"><span class="ruby-comment">=begin
 test embdoc
 =end</span>
 </pre>