Remove references to createClass in createElement docs (#8064)

docs/reference-react.md

@@ -139,12 +139,11 @@ React.createElement(
 )
 ```
 
-Create and return a new React element of the given type. The type argument can be either an
-html tag name string (eg. 'div', 'span', etc), or a React class (created via `React.createClass()`).
+Create and return a new [React element](/react/docs/rendering-elements.html) of the given type. The type argument can be either a tag name string (such as `'div'` or `'span'`), or a [React component](/react/docs/components-and-props.html) type (a class or a function).
 
-Code written with JSX will be converted to use `React.createElement()`. You will not typically invoke `React.createElement()` directly if you are using JSX. See [React Without JSX](/react/docs/react-without-jsx.html) to learn more.
+Convenience wrappers around `React.createElement()` for DOM components are provided by `React.DOM`. For example, `React.DOM.a(...)` is a convenience wrapper for `React.createElement('a', ...)`. They are considered legacy, and we encourage you to either use JSX or use `React.createElement()` directly instead.
 
-Convenience wrappers around `React.createElement()` for DOM components are provided by `React.DOM`. For example, `React.DOM.a(...)` is a convenience wrapper for `React.createElement('a', ...)`.
+Code written with [JSX](/react/docs/introducing-jsx.html) will be converted to use `React.createElement()`. You will not typically invoke `React.createElement()` directly if you are using JSX. See [React Without JSX](/react/docs/react-without-jsx.html) to learn more.
 
 * * *
 
@@ -178,7 +177,9 @@ This API was introduced as a replacement of the deprecated `React.addons.cloneWi
 React.createFactory(type)
 ```
 
-Return a function that produces React elements of a given type. Like [`React.createElement()`](#createElement), the type argument can be either an html tag name string (eg. 'div', 'span', etc), or a React class.
+Return a function that produces React elements of a given type. Like [`React.createElement()`](#createElement), the type argument can be either a tag name string (such as `'div'` or `'span'`), or a [React component](/react/docs/components-and-props.html) type (a class or a function).
+
+This helper is considered legacy, and we encourage you to either use JSX or use `React.createElement()` directly instead.
 
 You will not typically invoke `React.createFactory()` directly if you are using JSX. See [React Without JSX](/react/docs/react-without-jsx.html) to learn more.