+---------------------------------+
|     SYS(2021, <expN1>           |
|           [, <expN2> | <expC>])     |
+---------------------------------+

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Returns filter expression of an open single-entry .IDX index file, or
filter expressions for tags in compound .CDX index files.
Return value - Character
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You can create filtered indexes in FoxPro.  If you include the optional
FOR <expL> clause in INDEX, the index file acts as a filter on the
database.  Only records that match the filter expression <expL> are
available for display and access -- index keys are created in the index
file for just those records matching the filter expression.

SYS(2021) returns the filter expression of an open single-entry .IDX
index file, or the filter expressions for tags in compound .CDX index
files.  If the index is created without a FOR clause, the null string is
returned.

USE and SET INDEX both support an index file list that lets you open
index files for a database.  Any combination of single-entry .IDX index
files, structural compound or independent compound index files may be
included in the index file list.

Clauses
-------

<expN1>
        The numeric expression <expN1> specifies which filter expression to
return from the open index files or tags.  SYS(2021) returns filter
expressions from open index files and tags in the following order:

        . Filter expressions from single-entry .IDX index files (if any are
open) are returned first.  The order the single-entry index files are
included in USE or SET INDEX determines the order the filter expressions
are returned.

        . Filter expressions for each tag in the structural compound index (if
one is present) are returned next.  The filter expressions are returned
from the tags in the order the tags are created in the structural index.

        . Filter expressions for each tag in any open independent compound
indexes are returned last.  The filter expressions are returned from the
tags in the order the tags are created in the independent compound
indexes.

        The null string is returned if <expN1> is greater than the total number
of open single-entry .IDX files and structural compound and independent
compound index tags.

<expN2> | <expC>
        Filter expressions are returned from index files open in the currently
selected work area unless you include an optional work area or alias.
To return filter expressions from index files open in a specific work
area, include the work area number <expN2>, or the database alias
<expC>.  If a database doesn't have the alias you specify, the message
"Alias not found" is displayed.

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See Also:  CDX(), KEY(), INDEX, MDX(), NDX(), REINDEX, SET INDEX, SET
ORDER, SYS(), TAG()

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