this are the resource-tags (and some others)
https://rtfm.modx.com/revolution/2.x/making-sites-with-modx/commonly-used-template-tags
Resource-tags and TV-tags of the current resource start with
Placeholders can be set by snippets or plugins for example with the API-method setPlaceholder or with sending properties to a chunk with the getChunk-method.
Each snippet has its own set of placeholders.
Placeholders start with [[+
They can also be injected to chunks, for example
[[$base_template? &myplaceholder=`Test`]]
Then you can use
in the chunk 'base_template'
Regarding Tagger. Personally I use tagger, too. IMO, it is the best option for tagging resources.
Collections are nothing else, than Resources.
It is just another way to organize resources.
They are shown in a nice grid instaed in the resource-tree.
This is a good solution, if you have many resources of the same kind under one parent-resource.
MIGX (the MIGX-TV) stores its items as one json-string into a TV-value.
This is nice, if you need to add some items,
- for example images with title and description
- chunklists for the sidebar(think kind of widgets)
- external or internal linklists
or any other kind of small listings
And then there is MIGXdb (included with MIGX)
With MIGXdb you can manage records of your own custom-tables or internal MODX-tables (also resources)
either within a TV-grid
or
within a Custom-Manager-Page (CMP)