Feature: #100254 - Support download attribute in file link browser 

Description 

The HTML5 download attribute can now be configured per link in the file link browser. When set, the browser will force a file download instead of navigating to the file URL.

The link browser renders a "Force download" checkbox for file links. When enabled, an optional "Custom filename" text field appears, allowing editors to specify an alternative filename for the downloaded file.

The TypoLink codec supports an optional seventh TypoLink segment for download. The value true produces a boolean download attribute ( <a download>), while any other string value produces a named download attribute ( <a download="custom-name.pdf">).

Example TypoLink strings:

t3://file?uid=42 - - - - - true
t3://file?uid=42 - - - - - report.pdf

Impact 

Editors can now control per link whether a file should be downloaded or displayed in the browser. This works in both the RTE and non-RTE link browser dialogs.

Existing TypoLink values without download remain unchanged and continue to work as before.