Describe the bug
advancedFormat and buddhistEra plugins are changing/interpolating content inside square brackets

// with advancedFormat
const dayJSformat = dayjs.format('[Saturday]') // outputs: outputs something like "1418400000aturday"
const momentFormat = moment.format('[Saturday]') // outputs: "Saturday"
expect(dayJSformat).toEqual(momentFormat) // throws

Expected behavior
any plugins extending the format method interpolation should uphold behavior of the original format method and not change/interpolate content inside square brackets

Information

• Day.js Version: all
• OS: all
• Browser: all