We are leveling up the text_area, not the text_field, so match names

README.md

@@ -41,7 +41,7 @@ Assumes a Rails 5.2+ application with Active Storage and Webpacker installed.
     end
     ```
 
-1. Replace form `text_area`s with `rich_text_field`s:
+1. Replace form `text_area`s with `rich_text_area`s:
 
     ```erb
     <%# app/views/messages/_form.html.erb %>
@@ -49,7 +49,7 @@ Assumes a Rails 5.2+ application with Active Storage and Webpacker installed.
       …
       <div class="field">
         <%= form.label :content %>
-        <%= form.rich_text_field :content %>
+        <%= form.rich_text_area :content %>
       </div>
       …
     <% end %>

app/helpers/action_text/tag_helper.rb

@@ -2,7 +2,7 @@ module ActionText
   module TagHelper
     cattr_accessor(:id, instance_accessor: false) { 0 }
 
-    def rich_text_field_tag(name, value = nil, options = {})
+    def rich_text_area_tag(name, value = nil, options = {})
       options = options.symbolize_keys
 
       options[:input] ||= "trix_input_#{ActionText::TagHelper.id += 1}"
@@ -26,7 +26,7 @@ def render
       options = @options.stringify_keys
       add_default_name_and_id(options)
       options["input"] ||= dom_id(object, [options["id"], :trix_input].compact.join("_"))
-      @template_object.rich_text_field_tag(options.delete("name"), editable_value, options)
+      @template_object.rich_text_area_tag(options.delete("name"), editable_value, options)
     end
 
     def editable_value
@@ -35,14 +35,14 @@ def editable_value
   end
 
   module FormHelper
-    def rich_text_field(object_name, method, options = {})
+    def rich_text_area(object_name, method, options = {})
       Tags::ActionText.new(object_name, method, self, options).render
     end
   end
 
   class FormBuilder
-    def rich_text_field(method, options = {})
-      @template.rich_text_field(@object_name, method, objectify_options(options))
+    def rich_text_area(method, options = {})
+      @template.rich_text_area(@object_name, method, objectify_options(options))
     end
   end
 end

test/dummy/app/views/messages/_form.html.erb

@@ -18,7 +18,7 @@
 
   <div class="field">
     <%= form.label :content %>
-    <%= form.rich_text_field :content, class: "trix-content" %>
+    <%= form.rich_text_area :content, class: "trix-content" %>
   </div>
 
   <div class="actions">