Modern XML toolchains include advanced features that support XML editing including schema validation and schema-aware editing. The templates provided at Templates and schemas contain the necessary code to make this work.
The following XML toolchains have been reported as in use by IETF community members. These are all interactive XML editors.
The popular open source editor Emacs includes nXML Mode, which enables validation and schema-sensitive editing when you use an RNC schema.
Oxygen XML Editor is a commercial XML editor. This tool comes in different versions with a number of different licensing options, though all versions support RELAX NG validation and some support syntax highlighting and intelligent auto-completion. The premium version also supports collaborative edIting, including tracked changes and comment review.
The same company also makes Oxygen Content Fusion, which support web-based collaborative editing and document review.
XMLmind XML Editor (XXE) is a commercial near-WYSIWYG XML editor with a free edition for personal use. XXE supports RNC schema validation and context-sensitive editing.
A community developed configuration for XXE, xml2rfc-xxe is available, providing additional context-sensitive editing features, however this does not support the latest version of RFCXML and is unsupported.
IETF community members report using a range of text editors with varying support for XML editing, and and validating the RFCXML externally using xmllint, a common open source, command line tool.
Authors writing in XML may find the following tools helpful:
Drafting in Markdown describes the use of the i-d-template and internet-draft-template projects for managing I-Ds. These tools can be used to manage RFCXML I-Ds, with most of the same automation features.