There&#39;s precious little documentation about the `declare-styleable` tag by which we can declare custom styles for components. I did find [this list][1] of valid values for the `format` attribute of the `attr` tag. While that&#39;s nice as far as it goes, it doesn&#39;t explain how to use some of those values. Browsing [attr.xml][2] (the Android source for the standard attributes), I discovered that you can do things like:

    &lt;!-- The most prominent text color.  --&gt;
    &lt;attr name=&quot;textColorPrimary&quot; format=&quot;reference|color&quot; /&gt;

The `format` attribute can evidently be set to a combination of values. Presumably the `format` attribute helps the parser interpret an actual style value. Then I discovered this in attr.xml:

    &lt;!-- Default text typeface. --&gt;
    &lt;attr name=&quot;typeface&quot;&gt;
        &lt;enum name=&quot;normal&quot; value=&quot;0&quot; /&gt;
        &lt;enum name=&quot;sans&quot; value=&quot;1&quot; /&gt;
        &lt;enum name=&quot;serif&quot; value=&quot;2&quot; /&gt;
        &lt;enum name=&quot;monospace&quot; value=&quot;3&quot; /&gt;
    &lt;/attr&gt;
    
    &lt;!-- Default text typeface style. --&gt;
    &lt;attr name=&quot;textStyle&quot;&gt;
        &lt;flag name=&quot;normal&quot; value=&quot;0&quot; /&gt;
        &lt;flag name=&quot;bold&quot; value=&quot;1&quot; /&gt;
        &lt;flag name=&quot;italic&quot; value=&quot;2&quot; /&gt;
    &lt;/attr&gt;

Both of these seem to declare a set of allowed values for the indicated style.

So I have two questions:

1. What&#39;s the difference between a style attribute that can take on one of a set of `enum` values and one that can take on a set of `flag` values?
2. Does anyone know of any better documentation for how `declare-styleable` works (other than reverse engineering the Android source code)?

  [1]: http://chaosinmotion.com/blog/?p=179
  [2]: https://android.googlesource.com/platform/frameworks/base/+/master/core/res/res/values/attrs.xml


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Declaring styleable attributes in Android