# User Grammar Extensions

In some cases, the PHI grammar files provide entities for values that are very broad, to allow you to find values that do not have very well-defined formats. To reduce the number of false positives in these cases, only the context form of the entity is available by default (that is, with a suitable landmark).

You can use a user extension to expand the entity to include more specific formats, which enables the `nocontext` entity.

## Medical Record Numbers

Medical Record Numbers (MRN) are provider-specific, and have a large number of possible formats. Therefore, the provided MRN entities in the `healthplan.ecr` grammar are generic, and matches a string of 7-15 alphanumeric characters, with optional - and / separators.

Because the MRN pattern is so broad, it can match a lot of values that are not actually MRNs. To reduce the number of false positives, only the context form of the entity is available by default (that is, with a suitable landmark).

If you have a specific set of MRN values with well-defined patterns that you want to match, you can use the `healthplan_user.xml` extension grammar. This XML file allows you to expand the MRN grammar with more specific patterns, and compile them into a grammar. In this case, the original `context` entity is available, with your additional entities, and it also enables the `nocontext` entity.

For details of how to expand and compile the user XML grammar, refer to the Eduction User and Programming Guide.

## Generic License Numbers

The generic entities in the `license.ecr` grammar attempt to match a variety of different license numbers. The `phi/license/generic` entity matches a string of 5-20 alphanumeric characters (which must include at least one number), with optional - and / separators.

If you have a specific set of license values with well-defined patterns that you want to match, you can use the `license_user.xml` extension grammar. This XML file allows you to expand the grammar with more specific patterns, and compile them into a grammar. In this case, the original `context` entity is available, with your additional entities, and it also enables the `nocontext` entity.

For details of how to expand and compile the user XML grammar, refer to the Eduction User and Programming Guide.

## Generic Certificate Numbers

The generic entities in the `certificate.ecr` grammar attempt to match a variety of different license numbers. The `phi/certificate/generic` entity matches a string of 5-20 alphanumeric characters (which must include at least one number), with optional - and / separators.

If you have a specific set of certificate values with well-defined patterns that you want to match, you can use the `certificate_user.xml` extension grammar. This XML file allows you to expand the grammar with more specific patterns, and compile them into a grammar. In this case, the original `context` entity is available, with your additional entities, and it also enables the `nocontext` entity.

For details of how to expand and compile the user XML grammar, refer to the Eduction User and Programming Guide.

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