12 files declare their use of LinkRelBase in Metatag 8

AndroidAppLinkAlternative.php in metatag_mobile/src/Plugin/metatag/Tag/AndroidAppLinkAlternative.php

AppleTouchIcon.php in metatag_favicons/src/Plugin/metatag/Tag/AppleTouchIcon.php

AppleTouchIconPrecomposed.php in metatag_favicons/src/Plugin/metatag/Tag/AppleTouchIconPrecomposed.php

Author.php in metatag_google_plus/src/Plugin/metatag/Tag/Author.php

HreflangBase.php in metatag_hreflang/src/Plugin/metatag/Tag/HreflangBase.php

IosAppLinkAlternative.php in metatag_mobile/src/Plugin/metatag/Tag/IosAppLinkAlternative.php

LinkMediaBase.php in metatag_mobile/src/Plugin/metatag/Tag/LinkMediaBase.php

LinkSizesBase.php in metatag_favicons/src/Plugin/metatag/Tag/LinkSizesBase.php

MaskIcon.php in metatag_favicons/src/Plugin/metatag/Tag/MaskIcon.php

Publisher.php in metatag_google_plus/src/Plugin/metatag/Tag/Publisher.php

ShortcutIcon.php in metatag_favicons/src/Plugin/metatag/Tag/ShortcutIcon.php

WebManifest.php in metatag_mobile/src/Plugin/metatag/Tag/WebManifest.php