src/vs/editor/common/languages/supports/tokenization.ts/ThemeTrieElementRule/acceptOverwrite
class ThemeTrieElementRule:	public acceptOverwrite(fontStyle: FontStyle, foreground: ColorId, background: ColorId): void {
		if (fontStyle !== FontStyle.NotSet) {
			this._fontStyle = fontStyle;
		}
		if (foreground !== ColorId.None) {
			this._foreground = foreground;
		}
		if (background !== ColorId.None) {
			this._background = background;
		}
		this.metadata = (
			(this._fontStyle << MetadataConsts.FONT_STYLE_OFFSET)
			| (this._foreground << MetadataConsts.FOREGROUND_OFFSET)
			| (this._background << MetadataConsts.BACKGROUND_OFFSET)
		) >>> 0;
	}