A widget that implements this interface can be configured to be aligned according to its contents' direction, in addition to the static alignment options offered by {@link HasHorizontalAlignment}.

abstract class HasAutoHorizontalAlignment extends HasHorizontalAlignment {
 /**
  * Specifies that the widget's contents should be aligned left for LTR
  * content, right for RTL content, and if the content's direction is DEFAULT,
  * like {@link #ALIGN_LOCALE_START}.
  */
 static const AutoHorizontalAlignmentConstant ALIGN_CONTENT_START = const AutoHorizontalAlignmentConstant.internal();

 /**
  * Specifies that the widget's contents should be aligned right for LTR
  * content, left for RTL content, and if the content's direction is DEFAULT,
  * like {@link #ALIGN_LOCALE_END}.
  */
 static const AutoHorizontalAlignmentConstant ALIGN_CONTENT_END = const AutoHorizontalAlignmentConstant.internal();

 /**
  * Gets the horizontal auto-alignment setting. This may be one of the
  * auto-alignment values above that depend on content direction (e.g.
  * {@link HasAutoHorizontalAlignment#ALIGN_CONTENT_START}), or one of the
  * "static" {@link HasHorizontalAlignment.HorizontalAlignmentConstant}
  * alignment values (e.g. {@link HasHorizontalAlignment#ALIGN_LOCALE_START}).
  * It may be set by either {@code setAutoHorizontalAlignment} or {@code
  * HasHorizontalAlignment#setHorizontalAlignment}. The default is null,
  * indicating that no specific horizontal alignment has been set, allowing it
  * to be determined by the usual HTML and CSS mechanisms.
  *
  * @return the current automatic horizontal alignment policy.
  */
 AutoHorizontalAlignmentConstant getAutoHorizontalAlignment();

 /**
  * Sets the horizontal alignment, allowing in addition to the "static"
  * {@link HasHorizontalAlignment.HorizontalAlignmentConstant} values, the
  * "automatic" {@link HasHorizontalAlignment.AutoHorizontalAlignmentConstant}
  * values that depend on the content direction. Determines the values returned
  * by both {@link #getAutoHorizontalAlignment} and
  * {@link HasHorizontalAlignment#getHorizontalAlignment()}.
  * <p> For the {@code ALIGN_CONTENT_START} and {@code ALIGN_CONTENT_END}
  * values, sets the horizontal alignment (including the value of {@code
  * HasHorizontalAlignment#getHorizontalAlignment()}) to the start or end edge
  * of the current content's direction, respectively, and continues to
  * automatically update it whenever the content direction changes.
  * <p> For other values, operates like {@link #setHorizontalAlignment}.
  * <p> For {@code null}, the horizontal alignment is cleared, allowing it to
  * be determined by the standard HTML mechanisms such as inheritance and CSS
  * rules.
  * @see HasHorizontalAlignment
  *
  * @param autoHorizontalAlignment the new automatic horizontal alignment
  *        policy
  */
 void setAutoHorizontalAlignment(AutoHorizontalAlignmentConstant autoHorizontalAlignment);
}