IPython.display HTML is overwriting the target attribute in hyperlinks

[michaele4321]

Describe the bug
When using iPython.Display HTML in Jupyter Lab code, the target attribute in hyperlinks is being overwritten with "_self" or"_blank"

To Reproduce
Steps to reproduce the behavior:

1. Open a new Jupyter Labs notebook with a Python3 kernel
2. enter and run

from IPython.display import HTML, display
sampleHtml = '<a target="jupyter_docs" href = "https://jupyterlab.readthedocs.io/en/stable/">Jupyter Docs</a>'
display(HTML(sampleHtml))

3. The following link is created

<a target="_blank" href="https://jupyterlab.readthedocs.io/en/stable/" rel="noopener">Jupyter Docs</a>

Expected behavior
The link should be

<a target="jupyter_docs" href="https://jupyterlab.readthedocs.io/en/stable/" rel="noopener">Jupyter Docs</a>

Desktop (please complete the following information):

• OS: macOS Sierra 10.12
• Browser chrome 75.0
• JupyterLab 1.0.0

Additional context
I'm not familiar enough with the Jupyter Lab code architecture to debug this but there is code in packages/rendermime/src/renderers.ts which looks like it might cause this problem.

if (isLocal) {
        el.target = '_self';
      } else {
        el.target = '_blank';
        el.rel = 'noopener';
      }

The HTML spec specifies that target allows values that are valid browsing context names or keywords which in practice means _blank, _self, _parent, _top, or anything else that does not start with a _.

[ian-r-rose]

Hi @michaele4321, the adding of _blank to links is deliberate (as you note by linking to the code). We want external links to open in a new tab. May I ask the reason for adding a browsing context manually?

That said, I think it is reasonable for us to not override the target if the user has explicitly added the attribute to a link. I think adding that check would be a reasonable fix for a new contributor. One would go to this part of the code where we add the _blank target, and check to see if the element already has a target attribute:

jupyterlab/packages/rendermime/src/renderers.ts

Lines 600 to 605 in 079115d

	if (isLocal) {
	el.target = '_self';
	} else {
	el.target = '_blank';
	el.rel = 'noopener';
	}

One would then not override the target attribute if it was already specified.

[michaele4321]

Hi @ian-r-rose, thanks for looking at this. The context is that I am generating an HTML table of data with each row linked to an external page. I want to use a named target so that each link opens in the same external page (in my case on a second screen) rather than opening multiple new tabs.

[ian-r-rose]

Interesting, thanks for sharing @michaele4321!

[kavishdahekar]

I'd like to take this issue up.

[blink1073]

Great, thanks @kavishdahekar!

[kavishdahekar]

Unable to add reviewers for PR #7215 .
@ian-r-rose , @blink1073 could any of you please take a look? Thanks.