Overridden method from original directive. For simple text nodes, it just invokes the base method. For complex nodes, it builds translation key from whole inner HTML and replaces it with its translation. This prevents splitting HTML into pieces and attempting to translate each one separately which doesn't work, because we extract strings in whole.

When this directive encounters element that is HTML, it should switch to Html mode even if new translated element does not contain any HTML.

Used to trigger events when html is replaced by directive.

When this directive successfully translates node, it stores its value in this property. Another translation will be performed only if new translation value differs from stored one.