When creating your own theme for Publli, you maybe want to list all posts regarding to one tag on a single page. This can be achieved by the following:

1. create an override folder as descibed here: https://getpublii.com/dev/theme-overrides/

2. copy the config.json from the original theme folder to the overrride folder and add something like

"postTemplates": {
  "portfolio": "portfolio filter"
},

as described here: https://cv.domagic.site/posts/alternative-post-template-with-filter-for-publii-cms

3. duplicate the index.hbs and move this copy to the override folder. Rename it to post-newname.hbs, as described here: https://getpublii.com/dev/how-to-create-custom-templates/

4. The post-newname.hbs now can be used as a post template. Create a post and choose the template: 

5. I built this template to show all posts regarding my trip to Mallorca, so I named the post template "mallorca filter", as it shows posts with the tag 'Mallorca', only.

To achieve this, follow the instructions: https://getpublii.com/dev/how-to-display-posts-connected-with-a-specific-tag-name/

Find the the {{#each post}} helper and replace it with 

{{#each @website.contentStructure.tags}}

and add 

{{#checkIf this.name '==' 'TAGNAME'}}
    {{/each}}
    {{#if this.postsNumber}}
    {{#each this.posts}}

Replace TAGNAME with the tag you want to show/filter. Use the name, not the slug, in my case Mallorca, not mallorca.

Find the closing helper part {{/each}} (from the the {{#each post}} above) and put the following code right before the helper:

{{/each}}
{{/if}}
{{/checkIf}}