Rmarkdown does not recognize pandoc filter - filter

Question

I would like to call a pandoc filter (this one) from rmarkdown/RStudio. However, pandoc seems not to recognize the filter. I've handed over the filter in the YAML header. Consider this rmd file:
---
title: "test"
output: pdf_document
header-includes:
- \usepackage{xspace}
pandoc_args:
- --filter
- pandoc-filter/typography.py
---
test
s.S.
The knitting output shows no sign that the filter was handed over to pandoc:
/usr/local/bin/pandoc +RTS -K512m -RTS test_typography-py.utf8.md --to latex --from markdown+autolink_bare_uris+ascii_identifiers+tex_math_single_backslash --output test_typography-py.pdf --template /Library/Frameworks/R.framework/Versions/3.4/Resources/library/rmarkdown/rmd/latex/default-1.17.0.2.tex --highlight-style tango --pdf-engine pdflatex --variable graphics=yes --variable 'geometry:margin=1in'
The rendered pdf file does not show the effects of the filter, see image
(The effect of the filter is to render a thin space between phrases such as "z.B." or "e.g.".)
What can I do to get this filter run by pandoc via rmarkdown (preferably using the YAML header)?

Answer 1

I just realized (thanks to #NMarkgraf) that I had an intendation error. The correct intendation in YAML is this:
---
title: "test"
header-includes:
- \usepackage{xspace}
output:
pdf_document:
pandoc_args:
- --filter
- typography.py
---
Then it works - the filter is recognized.