Question: I need a solution that offers intelligent XML editing with features like content completion and tree-based outline views.

If you're looking for a tool with smart XML editing abilities like content completion and tree-based outline views, Oxygen XML Editor is a great option. It's a full-featured, cross-platform tool for XML authoring and development, with advanced smart XML editing abilities like content completion and a tree-based outline view. It also supports other XML-related technologies like XSL/XSLT and single-source XML publishing with visual WYSIWYG editing.

Another option is Altova, which includes XMLSpy, a professional XML and JSON editor with tools for modeling, editing, transforming and debugging. XMLSpy has advanced XML editing abilities, but it also handles other data formats like JSON and relational databases, so it can be a good option for your needs.

If you're looking for a more coding-oriented tool, IntelliJ IDEA is a powerful Integrated Development Environment (IDE) for multiple programming languages and frameworks. Although it's geared for Java and Kotlin programmers, its knowledge of code and AI-powered help can be useful for anyone, so it's a good option if you need a more complete coding environment.

If you want a flexible, real-time collaboration tool, Tiptap is a headless content editor and collaboration framework. It supports real-time collaboration, AI-generated content and version control, so it's a good foundation for building custom content experiences and collaborative platforms.