SelectVariants (Documentation): Purpose of reference sequence

[J-Moravec]

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In the documentation for the SelectVariants tool, it isn't clear what does -R do.

The documentation for the -R is empty, it is set as an optional parameter, but both examples on the page do set it.

https://gatk.broadinstitute.org/hc/en-us/articles/360036362532-SelectVariants

On the other hand, examples mentioned elsewhere ignore reference sequence when calling SelectVariants.

https://gatk.broadinstitute.org/hc/en-us/articles/360035531112--How-to-Filter-variants-either-with-VQSR-or-by-hard-filtering