If you use Magefan Blog Extension on Magento 2.2.x or greater and receive the error message:

1 exception(s):
Exception #0 (Magento\Framework\Config\Dom\ValidationException): Element 'block', attribute 'class': [facet 'pattern'] The value '\Magento\Framework\View\Element\Text\ListText' is not accepted by the pattern '[A-Z][_a-zA-Z\d]*(\\[A-Z][_a-zA-Z\d]*)*'.
Line: 982

Element 'block', attribute 'class': '\Magento\Framework\View\Element\Text\ListText' is not a valid value of the atomic type 'blockClassType'.
Line: 982


Exception #0 (Magento\Framework\Config\Dom\ValidationException): Element 'block', attribute 'class': [facet 'pattern'] The value '\Magento\Framework\View\Element\Text\ListText' is not accepted by the pattern '[A-Z][_a-zA-Z\d]*(\\[A-Z][_a-zA-Z\d]*)*'.
Line: 982

Element 'block', attribute 'class': '\Magento\Framework\View\Element\Text\ListText' is not a valid value of the atomic type 'blockClassType'.
Line: 982

First please make sure that you have updated the blog extension to the newest version. Then check all custom blog layout files in your theme (app/code/design/ThemeVendor/themename/Magefan_Blog/layout), they may have a code e.g.:

class="\Magento

you need to change it to

class="Magento

Then flush Magento cache.