alx25 opened a new issue, #35182:
URL: https://github.com/apache/superset/issues/35182
### Bug description
After upgrading from Superset 4.1.2 to 5.0 and now 6.0, my Handlebars-based
custom charts stopped rendering HTML. The template output is being HTML-escaped
by the frontend sanitizer (e.g., <ul>, <li>, quotes) so the chart shows raw
text instead of rendered elements. In 4.1.2 this template rendered correctly.
Steps to Reproduce
1. Create a simple dataset.
2. Add a Handlebars chart and set the template and CSS:
```
<ul class="data-list">
{{#each data}}
<li>{{stringify this}}</li>
{{/each}}
</ul>
```
CSS:
`.data-list { background-color: yellow; }
`
Expected Behavior
The template should render valid HTML (a yellow list with <li> items) as it
did in Superset 4.1.2.
Actual Behavior
In 5.0 and 6.0, the output appears escaped (e.g., <ul
class="data-list"> ...) and is displayed as plain text. CSS is not
applied because the markup never becomes DOM elements.
### Screenshots/recordings
- Superset 4.1.2 (works): Handlebars output renders as a styled <ul> list
(yellow background) with each row serialized into <li> items.
<img width="1022" height="771" alt="Image"
src="https://github.com/user-attachments/assets/3039b932-0d5d-412a-b8f9-588da02a6e7e";
/>
- Superset 6.0 (broken): The same output is escaped and shown as a long text
line with <ul>, <li>, and " entities; CSS has no effect.
<img width="2197" height="667" alt="Image"
src="https://github.com/user-attachments/assets/408a69df-a0c4-4e44-a2f0-16caa2407673";
/>
### Superset version
5.0.0
### Python version
3.11
### Node version
16
### Browser
Chrome
### Additional context
Install: pip in a Python venv
### Checklist
- [x] I have searched Superset docs and Slack and didn't find a solution to
my problem.
- [x] I have searched the GitHub issue tracker and didn't find a similar bug
report.
- [x] I have checked Superset's logs for errors and if I found a relevant
Python stacktrace, I included it here as text in the "additional context"
section.
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