A source code to demo applying attributed strings attribute from markdown styles

CustomAttributedStringTextView.swift

//
//  CustomAttributedStringTextView.swift
//  SwiftUIBlogPosts
//
//  Created by Jayesh Kawli on 8/31/22.
//

import SwiftUI

struct CustomAttributedStringTextViewModel {

    let customAttributedInputString: AttributedString

    init() {
        let inputString = "^[Amsterdam](cityStyle: 'amsterdamStyle', cityColor: 'amsterdamColor') is a great city and ^[regular rainbow style](rainbowStyle: 'regular') awesome city to live in ^[first half rainbow style](rainbowStyle: 'firstHalf') or ^[second half rainbow style](rainbowStyle: 'secondHalf')"

        self.customAttributedInputString = (try? AttributedString(
            markdown: inputString,
            including: AttributeScopes.CustomCityAttributes.self,
            options: AttributedString.MarkdownParsingOptions(allowsExtendedAttributes: true))) ?? AttributedString(inputString)
    }
}

struct CustomAttributedStringTextView: View {

    let customAttributedStringTextViewModel: CustomAttributedStringTextViewModel

    init() {
        self.customAttributedStringTextViewModel = CustomAttributedStringTextViewModel()
    }

var body: some View {
    Text(customStyledAttributedString(input: customAttributedStringTextViewModel.customAttributedInputString))
        .padding()
}

private func customStyledAttributedString(input: AttributedString) -> AttributedString {

    var output = input

    for run in output.runs {

        let customCityAttributes = run.customCityAttributes

        guard customCityAttributes.customCityStyle != nil || customCityAttributes.customColorStyle != nil || customCityAttributes.customRainbowStyle != nil  else {
            continue
        }

        let range = run.range

        if let customCityStyle = customCityAttributes.customCityStyle {
            if customCityStyle == .amsterdamStyle {
                output[range].font = .largeTitle
            }
        }

        if let customColorStyle = customCityAttributes.customColorStyle {
            if customColorStyle == .amsterdamColor {
                output[range].foregroundColor = .orange
            }
        }

        if let customRainbowStyle = customCityAttributes.customRainbowStyle {

            let rainbowColorsCollection: [Color]

            switch customRainbowStyle {
            case .regular:
                rainbowColorsCollection = rainbowColorsCollectionFull
            case .firstHalf:
                rainbowColorsCollection = rainbowColorsCollectionFirstHalf
            case .secondHalf:
                rainbowColorsCollection = rainbowColorsCollectionSecondHalf
            }

            var integerIndex = 0
            for i in output[range].characters.indices {
                output[i..<output[range].characters.index(after: i)].foregroundColor = rainbowColorsCollection[integerIndex % rainbowColorsCollection.count]
                integerIndex += 1
            }
        }
    }

    return output
}

    private var rainbowColorsCollectionFull: [Color] {
        [.red, .orange, .yellow, .green, .blue, .indigo, .purple]
    }

    private var rainbowColorsCollectionFirstHalf: [Color] {
        [.red, .orange, .yellow]
    }

    private var rainbowColorsCollectionSecondHalf: [Color] {
        [.green, .blue, .indigo, .purple]
    }
}

public enum CustomCityStyleAttributes: CodableAttributedStringKey, MarkdownDecodableAttributedStringKey {
    public enum Value: String, Codable {
        case amsterdamStyle
    }

    public static var name = "cityStyle"
}

public enum CustomCityColorAttributes: CodableAttributedStringKey, MarkdownDecodableAttributedStringKey {
    public enum Value: String, Codable {
        case amsterdamColor
    }

    public static var name = "cityColor"
}

public enum CustomRainbowStyleAttributes: CodableAttributedStringKey, MarkdownDecodableAttributedStringKey {
    public enum Value: String, Codable {
        case regular
        case firstHalf
        case secondHalf
    }

    public static var name = "rainbowStyle"
}

public extension AttributeScopes {
    struct CustomCityAttributes: AttributeScope {
        let customCityStyle: CustomCityStyleAttributes
        let customColorStyle: CustomCityColorAttributes

        let customRainbowStyle: CustomRainbowStyleAttributes

        let swiftUI: SwiftUIAttributes
    }

    var customCityAttributes: CustomCityAttributes.Type  { CustomCityAttributes.self }
}

This (in gist) is far more easy to write than @-ing you in TT. 😃

^[string_to_decorate](attribute_key_1: attribute_value_1, attribute_key_2: attribute_value_2), this piece can be reinterpreted as ^[concept](semantic_this : … , style_that : … , annotation_for_classification: …) - think in CSS’s element’s class and style attributes. That will make the purpose of annotation not only for styling but also anything else (and potentially later re-styling)

This Apple’s markdown extension, supporting dictionary and more, is far more expressive than CSS’s class attribute’s merely flat string list.