The snippet based on SimplePie 1.3 which is already included in the package: 

Basic call: [ [ ! spiefeed ] ]

Documentation is here: http://rtfm.modx.com/display/ADDON/spieFeed

Installation Instructions

Install from Package Manager

1.6.2-pl (Mar 2, 2016)

• * [#15][#16] fixed stripHtmlTags
• * [#11][#12] fixed missing item level images
• * [#12] Fixed a simplepie bug "Call to a member function get_uri() on a non-object in " (see: simplepie/simplepie#214)
• * [#12] Added Dutch lexicon <https://github.com/vierkantemeter>

Version	Released	Author	Downloads
14 Versions		1 Contributors	6,748 Downloads
1.6.1-pl	Oct, 22 2012	goldsky	1,294
1.6.0-pl	Aug, 24 2012	goldsky	363
1.5.0-pl	Feb, 01 2012	goldsky	594
1.4.0-pl	Jan, 05 2012	goldsky	322
1.3-pl	Sep, 24 2011	goldsky	472
1.2.0-pl1	May, 12 2011	goldsky	502
1.1.0-pl	Jan, 22 2011	goldsky	681
1.1.0-rc1	Dec, 30 2010	goldsky	333
1.0.0-pl	Dec, 13 2010	goldsky	331
1.0.0-rc2	Dec, 06 2010	goldsky	312
1.0.0-beta2	Oct, 18 2010	goldsky	330
1.0.0-beta1	Oct, 18 2010	goldsky	272
1.0.0-rc1	Oct, 16 2010	goldsky	245