Custom CKEditor configuration including linebreak plugin

Custom.yaml

# Load default processing options
imports:
    - { resource: "EXT:rte_ckeditor/Configuration/RTE/Processing.yaml" }
    - { resource: "EXT:rte_ckeditor/Configuration/RTE/Editor/Base.yaml" }
    - { resource: "EXT:rte_ckeditor/Configuration/RTE/Editor/Plugins.yaml" }

# Add configuration for the editor
# For complete documentation see http://docs.ckeditor.com/#!/api/CKEDITOR.config
editor:
  externalPlugins:
    linebreak:
      resource: "EXT:basetemplate8/Resources/Public/JavaScript/Plugins/linebreak/plugin.js"

  config:
    extraAllowedContent: "*(*)[data-*]; span(shy)"
    
    # The default styles for the editor. You can add your custom styles here.
    contentsCss: ["EXT:rte_ckeditor/Resources/Public/Css/contents.css", "EXT:basetemplate8/Resources/Public/Css/rte_ckeditor.css"]
    stylesSet:
      # Alignment styles:
      - { name: "LLL:EXT:basetemplate8/Resources/Private/Language/rte.xlf:styles.align.left", element: ['h1', 'h2', 'h3', 'h4','h5', 'h6', 'p', 'td', 'th'], attributes: { 'class': 'text-left' }}
      - { name: "LLL:EXT:basetemplate8/Resources/Private/Language/rte.xlf:styles.align.center", element: ['h1', 'h2', 'h3', 'h4','h5', 'h6', 'p', 'td', 'th'], attributes: { 'class': 'text-center' }}
      - { name: "LLL:EXT:basetemplate8/Resources/Private/Language/rte.xlf:styles.align.right", element: ['h1', 'h2', 'h3', 'h4','h5', 'h6', 'p', 'td', 'th'], attributes: { 'class': 'text-right' }}
      - { name: "LLL:EXT:basetemplate8/Resources/Private/Language/rte.xlf:styles.align.justify", element: ['h1', 'h2', 'h3', 'h4','h5', 'h6', 'p', 'td', 'th'], attributes: { 'class': 'text-justify' }}

      # Block level styles:
      - { name: "LLL:EXT:basetemplate8/Resources/Private/Language/rte.xlf:styles.p.intro", element: "p", attributes: { 'class': 'intro' }}
      - { name: 'LLL:EXT:basetemplate8/Resources/Private/Language/rte.xlf:styles.list.checkmark', element: 'ul', attributes: { 'class': 'list--checkmark' } }

      # Inline styles:
      - { name: "LLL:EXT:basetemplate8/Resources/Private/Language/rte.xlf:styles.a.btn", element: "a", attributes: { 'class': 'btn' } }

    # Available block elements:
    format_tags: "p;h1;h2;h3;h4;pre"

    # Sort buttons:
    toolbarGroups:
      - { name: styles, groups: [ format, styles ] }
      - { name: colors }
      - { name: cleanup }
      - { name: basicstyles }
      - { name: align }
      - { name: list }
      - { name: links }
      - { name: paragraph, groups: [ indent, blocks ] }
      - { name: insert }
      - { name: clipboard, groups: [ clipboard, undo ] }
      - { name: table }
      - { name: tabletools }
      - { name: editing, groups: [ find, selection, spellchecker ] }
      - { name: tools }
      - { name: mode }
      - { name: linebreak }

    removeButtons:
      - Anchor
      - Underline
      - Strike
      - BGColor

    justifyClasses:
      - text-left
      - text-center
      - text-right
      - text-justify

    extraPlugins:
      - justify
      - specialchar
      - showblocks
      - colorbutton
      - find
      - linebreak

    removePlugins:
      - image

    # colorbutton config:
    colorButton_colorsPerRow: 8
    colorButton_colors: 'F26C4F,3A89C9,1B325F'

# Additional processing of tags inside the RTE:
processing:
  allowTags:
    - wbr

typoscript_setup.txt

// Allow <wbr> tag rendering in frontend:
lib.parseFunc.allowTags := addToList(wbr)
lib.parseFunc_RTE.allowTags := addToList(wbr)

// Remove any 'shy' classes from <span> elements:
lib.parseFunc_RTE.nonTypoTagStdWrap.HTMLparser.tags.span.fixAttrib.class.removeIfEquals = shy

// Remove all <span> elements which have no attribute:
lib.parseFunc_RTE.nonTypoTagStdWrap.HTMLparser.rmTagIfNoAttrib = span

// The same is needed for all occurrences inside lists:
lib.parseFunc_RTE.externalBlocks {
    ul {
        callRecursive = 1
        HTMLparser = 1
        HTMLparser.tags.span.fixAttrib.class.removeIfEquals = shy
        HTMLparser.rmTagIfNoAttrib = span
    }
    ol < .ul
}