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//! Style mix-in and other types.
//!
//! A [`Style!`](struct@Style) is an special widget that represents a set of properties that are dynamically loaded onto
//! another styleable widget. Styleable widgets inherit from [`StyleMix<P>`](struct@StyleMix) and provide a contextual
//! `style_fn` property that sets the widget style.
//!
//! Styles extend the contextual style by default, only replacing the intersection of properties.
//! The special [`replace`](struct@Style#method.replace) property can be set on a style to fully replace the contextual style.
//!
//! The example below demonstrates multiple contexts setting style for buttons.
//!
//! ```
//! use zng::prelude::*;
//! # let _app = APP.defaults();
//!
//! # let _ =
//! Stack! {
//! direction = StackDirection::top_to_bottom();
//! spacing = 5;
//!
//! zng::button::style_fn = Style! {
//! // override the default background_color for all buttons in the Stack.
//! // note that this does not override the hovered/pressed background.
//! widget::background_color = colors::BLUE;
//! };
//!
//! children = ui_vec![
//! // these buttons have the default style with blue background.
//! Button! { child = Text!("Default+BLUE") },
//! Button! { child = Text!("Default+BLUE") },
//!
//! Stack! {
//! direction = StackDirection::top_to_bottom();
//! spacing = 5;
//!
//! zng::button::style_fn = Style! {
//! // override the default border for all buttons in the Stack.
//! widget::border = 2, colors::GREEN;
//! };
//!
//! children = ui_vec![
//! // these buttons have the default style, with blue background and green border.
//! Button! { child = Text!("Default+BLUE+GREEN") },
//! Button! { child = Text!("Default+BLUE+GREEN") },
//!
//! Stack! {
//! direction = StackDirection::top_to_bottom();
//! spacing = 5;
//!
//!
//! zng::button::style_fn = Style! {
//! // override the context style background_color in the Stack.
//! widget::background_color = colors::RED;
//! };
//!
//! children = ui_vec![
//! // these buttons have the default style, with green border and red background.
//! Button! { child = Text!("Default+GREEN+RED") },
//! Button! { child = Text!("Default+GREEN+RED") },
//! // this button ignores the contextual style by setting the `style_fn` to a style
//! // that is `replace=true`.
//! Button! {
//! child = Text!("Default");
//! style_fn = zng::button::DefaultStyle!();
//! },
//! ]
//! },
//! ]
//! },
//! Stack! {
//! direction = StackDirection::top_to_bottom();
//! spacing = 5;
//!
//! zng::button::style_fn = Style! {
//! // replace the default style with this one.
//! replace = true;
//! widget::background_color = colors::RED;
//! };
//!
//! // these buttons only have the red background.
//! children = ui_vec![
//! Button! { child = Text!("RED") },
//! Button! { child = Text!("RED") },
//! ]
//! }
//! ]
//! }
//! # ;
//! ```
//!
//! # Shared Styles
//!
//! Style instances can be set directly on `style_fn` properties, but if the style is used by more then one widget property values
//! that can't be cloned will only appear on the last widget to use the style. The [`style_fn!`] macro can be used to declare a
//! closure that instantiates the style for each usage. The property values that can't be cloned are `impl UiNode` and `impl UiNodeList`.
//!
//! The example below demonstrates this issue:
//!
//! ```
//! use zng::prelude::*;
//! # let _scope = APP.defaults();
//!
//! # let _ =
//! Stack!(
//! top_to_bottom,
//! 20,
//! ui_vec![
//! Stack! {
//! direction = StackDirection::top_to_bottom();
//! spacing = 5;
//! widget::parallel = false; // init buttons sequentially
//!
//! zng::button::style_fn = Style! {
//! // background is `impl UiNode` that can't be cloned. Nodes
//! // are moved to the last place that requests it.
//! widget::background = zng::color::flood(colors::AZURE);
//! };
//! children = ui_vec![
//! Button! { child = Text!("Default") },
//! // the last button to init takes the background node.
//! Button! { child = Text!("Default+AZURE") },
//! ]
//! },
//! Stack! {
//! direction = StackDirection::top_to_bottom();
//! spacing = 5;
//!
//! // Sets the style to a closure that will be called for each button.
//! zng::button::style_fn = style_fn!(|_| Style! {
//! widget::background = zng::color::flood(colors::AZURE);
//! });
//! children = ui_vec![
//! // each button gets its own background node.
//! Button! { child = Text!("Default+AZURE") },
//! Button! { child = Text!("Default+AZURE") },
//! ]
//! }
//! ]
//! )
//! # ;
//! ```
pub use ;