validHashtag top-level constant

Implementation

const validHashtag =
    '($hashtagBoundary)'
    '($hashSigns)'
    r'(?!\uFE0F|\u20E3)'
    '($hashtagAlphaNumeric*$hashtagAlpha$hashtagAlphaNumeric*|[$hashtagEmoji]+)'
    '(?<![$hashtagConcatChars])';