The 'do NOT rainbowify big files' setting in the Rainbow Brackets plugin controls whether rainbow highlighting is applied to files that exceed a specified number of lines. This feature exists to prevent performance degradation when working with very large files, as syntax highlighting plugins can slow down the editor when processing files with many thousands of lines.

By default, this setting is enabled, and the maximum number of lines is set to 5000. When enabled, rainbow highlighting is skipped for any file larger than the configured threshold, improving performance and responsiveness for large files. If you disable this setting, rainbow highlighting will be applied to all files, regardless of size, which may negatively impact performance when editing very large files. You can adjust the threshold to suit your workflow if you want rainbow highlighting on larger files but still want to avoid performance issues with extremely large files. Reference

When a file exceeds the threshold and rainbowification is skipped, the plugin displays an editor banner. This banner includes a link that takes you directly to the settings interface, allowing you to quickly adjust the threshold or disable the restriction if needed.

To access and modify this setting through the plugin's interface:

1. Open your IDE's Settings or Preferences dialog (usually accessible via File > Settings on Windows/Linux or IntelliJ IDEA > Preferences on macOS).
2. Navigate to the Rainbow Brackets > Stop List.
3. Locate the option labeled "Do NOT rainbowify big files with more then xxx lines" (the exact label may vary slightly).
4. To enable the restriction, check the box; to disable it, uncheck the box.
5. If the restriction is enabled, set your preferred maximum number of lines in the associated input field (default is 5000).
6. Apply or OK your changes to save them. The plugin will immediately reflect your new settings.

If you open a file that is too large and rainbowify is skipped, use the banner's link to jump directly to these settings for quick adjustment.

For advanced users, these settings are stored in the plugin's configuration file as follows:

<option name="doNOTRainbowifyBigFiles" value="true" />
<option name="bigFilesLinesThreshold" value="5000" />

You can edit these values directly in the configuration XML if needed, but using the plugin's interface is recommended for most users.