the browser when visiting websites?
Or are these scriptlets some code running purely locally?
A scriptlet could ran from a remote url or a local url.
What programming language(s) are supported for these scriptlets?
HTML/DHTML and VBScript
A scriptlet is an HTML code file that has either an .sct or an .htm
extension. You can create scriptlets by using HTML code and VBScript
code, JScript code, or both, and you can create them in any HTML
A scriptlet is a lightweight, reusable Component Object Model (COM)
component that consists of HTML code and script and is created
according to certain conventions. A behavior is a lightweight
component that encapsulates specific functionality. When applied to an
HTML element, a behavior enhances the element's default behavior.
Scriptlets and behaviors are very similar in that they both contain
script in a separate document that exposes functionality that can be
used in a Web page. They differ in that behaviors are STYLE attributes
that point to a separate file containing script that is called in
response to an event associated with an HTML element. Scriptlets, on
the other hand, can be used for almost anything you can do with script
in a Web page.