queries docs

docs/guide/queries.md

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+# DOM Queries
+
+In the previous chapter we introduced the [DOM](../guide/CSS.md#the-dom), which represents the widgets in a Textual app. We saw how you can apply styles to the DOM with CSS *selectors*.
+
+Selectors are a very useful thing and can do more that apply styles. We can also modify widgets using selectors in a simple expressive way. Let's look at how!
+
+## Making queries
+
+Apps and widgets have a [query][textual.dom.DOMNode.query] method which finds (or queries) widgets. Calling this method will return a [DOMQuery][textual.css.query.DOMQuery] object which is a container (list-like) object with widgets you may iterate over.
+
+If you call `query` with no arguments, you will get back a `DOMQuery` containing all widgets. This method is *recursive*, meaning it will return all child widgets.
+
+Here's how you might iterate over all the widgets in your app:
+
+```python
+for widget in self.query():
+    print(widget)
+```
+
+Called on the `app`, this will retrieve all widgets in the app. If you call the same method on a widget, it will return children of that widget.
+
+### Query selectors
+
+You can also call `query` with a CSS selector. Let's look a few examples:
+
+If we want to find all the button widgets, we could do something like the following:
+
+```python
+for button in self.query("Button"):
+    print(button)
+```
+
+Any selector that works in CSS will work. For instance, if we want to find all the disabled buttons in a Dialog widget, we could do something like the following: 
+
+```python
+for button in self.query("Dialog > Button.disabled"):
+    print(button)
+```
+
+### First and Last
+
+The [first][textual.css.query.DOMQuery.first] and [last][textual.css.query.DOMQuery.last] methods will return the first and last widgets from the selector, respectively.
+
+Here's how we might find the last button in an app.
+
+```python
+last_button = self.query("Button").last()
+```
+
+If there are no buttons, textual will raise a [NoMatchingNodesError][textual.css.query.NoMatchingNodesError] exception. Otherwise it will return a button widgets.
+
+Both `first()` and `last()` accept an `expect_type` argument that should be the class of the widget you are expecting. For instance, lets say we want to get the last with class `.disabled`, and we want to check it really is a button. We could do this:
+
+```python
+disabled_button = self.query(".disables").last(Button)
+```
+
+The query selects all widgets with a `disabled` CSS class. The `last` method ensures that it is a `Button` and not any other kind of widget.
+
+If the last widget is *not* a button, Textual will raise a [WrongType][textual.css.query.WrongType] exception.
+
+!!! tip
+
+    Specifying the expected type allows type-checkers like MyPy to know the exact return type.
+
+### Filtering
+