# Preloading shared reference documents

An option is available in the `Configuration` to indicate that calls to the `doc()` or `document()` functions with constant string arguments should be evaluated when a query or stylesheet is compiled, rather than at run-time. This option is intended for use when a reference or lookup document is used by all queries and transformations. Using this option has a number of effects:

1. The URI is resolved using the compile-time URIResolver rather than the run-time URIResolver

2. The document is loaded into a document pool held by the `Configuration`, whose memory is released only when the `Configuration` itself ceases to exist;

3. all queries and transformations using this document share the same copy;

4. any updates to the document that occur between compile-time and run-time have no effect.

The option is selected by using `Configuration.setConfigurationProperty()`\ or `TransformerFactory.setAttribute()` with the property name `FeatureKeys.PRE_EVALUATE_DOC_FUNCTION`. This option is not available from the command line because it has no useful effect with a single-shot compile-and-run interface.

This option has no effect if the URI supplied to the `doc()` or `document()` function includes a fragment identifier.

It is also possible to preload a specific document into the shared document pool from the Java application by using the call `config.getDocumentPool().add(doc, uri)`. When the `doc()` or `document()` function is called, the shared document pool is first checked to see if the requested document is already present. The `DocumentPool` object also has a `discard()` method which causes the document to be released from the pool.

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