It's in the docs:
http://help.adobe.com/en_US/flex/using/WS2db454920e96a9e51e63e3d11c0bf680e1-7ffe.html#WS2db454920e96a9e51e63e3d11c0bf69084-7a2c
ArrayElementType metadata tag
When you define an Array variable in ActionScript, you specify Array as the
data type of the variable. However, you cannot specify the data type of the
elements of the Array.
To allow the Flex MXML compiler to perform type checking on Array elements,
you can use the [ArrayElementType] metadata tag to specify the allowed data
type of the Array elements, as the following example shows:
public class MyTypedArrayComponent extends VBox {
[ArrayElementType("String")]
public var newStringProperty:Array;
[ArrayElementType("Number")]
public var newNumberProperty:Array;
...
}
Note: The MXML compiler checks for proper usage of the Array only in MXML
code; it does not check Array usage in ActionScript code.
In this example, you specify String as the allowed data type of the Array
elements. If a user attempts to assign elements of a data type other than
String to the Array in an MXML file, the compiler issues a syntax error, as
the following example shows:
<MyComp:MyTypedArrayComponent>
<MyComp:newStringProperty>
<fx:Number>94062</fx:Number>
<fx:Number>14850</fx:Number>
<fx:Number>53402</fx:Number>
</MyComp:newStringProperty>
</MyComp:MyTypedArrayComponent>
In this example, you try to use Number objects to initialize the Array, so
the compiler issues an error.
You can also specify Array properties as tag attributes, rather than using
child tags, as the following example shows:
<MyComp:MyTypedArrayComponent newNumberProperty="[abc,def]"/>
This MXML code generates an error because Flex cannot convert the Strings
"abc" and "def" to a Number.
You insert the [ArrayElementType] metadata tag before the variable
definition. The tag has the following syntax:
[ArrayElementType("elementType")]
The following table describes the property of the [ArrayElementType]
metadata tag:
Property
Type
Description
elementType
String
Specifies the data type of the Array elements, and can be one of the
ActionScript data types, such as String, Number, class, or interface.
You must specify the type as a fully qualified class name, including the
package.
On Thu, Mar 2, 2017 at 6:10 AM, Harbs <harbs.li...@gmail.com> wrote:
> I just noticed a few places in TLF where we have such metadata. For
> example:
>
> [ ArrayElementType("text.elements.TextFlowLine") ]
> private var _lines:Array;
>
> Does anyone know what that does?
>
