# Textual constants.py — TEXTUAL_THEME environment default

## Metadata

| Field | Value |
|---|---|
| Institute | Molodetz Institute — Research & Retrieval Division |
| Subject | tui-framework-design |
| Document type | Source Dossier |
| Tier | 1 |
| Source title | Textual src/textual/constants.py — TEXTUAL_THEME env handling |
| Source URL | https://raw.githubusercontent.com/Textualize/textual/main/src/textual/constants.py |
| Source publisher / author | Textualize (Textual project) |
| Source type | repository |
| Source date (published) | Unknown — not stated |
| Date researched | 2026-10-11 |
| Researched by | tai (agent), model: Muse Spark, on behalf of retoor |
| Research method | direct page fetch |
| Confidence | Medium |
| Status | Active |

## Summary

A thin source with one finding: the `TEXTUAL_THEME` environment variable sets the default theme, taking a first-existing-wins list. It exists here as the precedent for tai's `TAI_THEME` variable.

## Key findings

- `TEXTUAL_THEME` sets the default theme from the environment, accepting a list where the first existing theme wins.

## Pros / strengths

- Env-var default with first-existing-wins fallback is a small, robust precedence mechanism worth copying exactly.

## Cons / limitations / caveats

- Thin source: one mechanism only, no interaction with flags or runtime switching visible here.

## Relevance to tai

- Direct precedent for the palette-role conclusion's precedence chain (flag > `TAI_THEME` env var > default).

## Changelog

| Date | Change |
|---|---|
| 2026-10-11 | Initial dossier created from 2026-10-11 research-pass evidence (body opened via web_fetch by researching agent). |