TOML users have had to manually enumerate every environment in env_list when they need a test matrix, while INI users could write concise expressions like py3{12,13}-django{42,50}. This gap made TOML configuration verbose and error-prone for projects with large matrices, and was one of the most visible feature disparities between the two formats.

✨ This introduces a TOML-native product dict syntax that leverages TOML's type system instead of mimicking INI's string-based brace expansion. Factor groups are expressed as arrays of strings or range dicts, and tox computes the Cartesian product joining combinations with -. Range dicts ({ prefix = "py3", start = 12, stop = 14 }) generate sequential factors, with open-ended bounds matching INI's py3{10-} behavior. An exclude key allows skipping specific combinations — a capability not available in INI at all.

env_list = [
    "lint",
    { product = [
        { prefix = "py3", start = 12, stop = 14 },
        ["django42", "django50"],
    ] },
]

Documentation has been updated across all four Diataxis dimensions (tutorial, how-to, reference, explanation) with TOML shown first in all tab pairs. The "TOML feature gaps" section has been renamed to "Format comparison" since generative env_list was the last major functional gap — only generative section names remain INI-exclusive. The JSON schema has been extended to validate product dicts with their factor groups and optional exclude arrays.