hashtagBoundary top-level constant

String const hashtagBoundary

This pattern captures the beginning (^), end ($), and certain specific characters that can be considered as boundaries for hashtags. These boundaries help in accurately extracting hashtags from text.

The components that make up this pattern are:

1. ^: Matches the start of a string.
2. \uFE0E, \uFE0F: Match variation selectors which are used to specify a specific glyph variant for a Unicode character (e.g., to differentiate between emoji-style and text-style for certain symbols).
3. $: Matches the end of a string.
4. (?!$hashtagAlphaNumeric|&): Negative lookahead assertion to ensure that what follows isn't an alphanumeric hashtag character or an ampersand (&).
5. $codePoint: Matches any valid Unicode code point, ensuring the boundary is set accurately with respect to the surrounding text.

Implementation

const hashtagBoundary = r'(?:^|\uFE0E|\uFE0F|$|(?!'
    '$hashtagAlphaNumeric|&)'
    '$codePoint)';