# Guidelines and requirements
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 When creating a filter expression, note the following guidelines and requirements: 
+ You can't use filters to include or exclude items based on unstructured textual item metadata such as product descriptions.
+ If you are filtering based on item or action interactions data, you can only filter based on event type. You can't filter based on other interaction metadata, such as contextual metadata.
+ Amazon Personalize ignores case only when matching event types.
+ You can't use Item Interaction and Item datasets in one expression. To create a filter that filters by Interaction and then Item datasets (or the opposite), you must chain two or more expressions together. For more information, see [Combining multiple expressions](multiple-expression-example.md). 
+ You can't use Item interaction and Action datasets in one expression. To create a filter that filters by Item interaction and then Action datasets (or the opposite), you must chain two or more expressions together. For more information, see [Combining multiple expressions](multiple-expression-example.md). 
+ You can't use item interactions filters with the [Item-Attribute-Affinity recipe](item-attribute-affinity-recipe.md). 
+  You can't create filter expressions that filter using values with a boolean type in your schema. To filter based on boolean values, use a schema with a field of type *String* and use the values `"True"` and `"False"` in your data. Or you can use type *int* or *long* and values `0` and `1`. 
+  The maximum number of distinct dataset fields for a filter, either in one expression or across multiple expressions chained together, is **10**. The maximum number of distinct dataset fields across all filters in a dataset group is **20**. 
+  You can apply a filter with the CurrentItem element only if your domain use case or custom recipe generates related items recommendations, such as the Similar-Items recipe or the *More Like X* domain use case. 
+ You can't use placeholder parameters in a filter expression that uses the NOT\$1IN operator. Instead, use the IN operator and use the opposite Action. For example, use Include instead of Exclude (or the reverse).
+ You can't create filters that filter based on `Action expiration timestamp` and `Repeat frequency` data. Amazon Personalize automatically filters action recommendations based on this data.