If you use Magento 2.2.x and get the error like:

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: 1187

Element 'block', attribute 'class': '\Magento\Framework\View\Element\Text\ListText' is not a valid value of the atomic type 'blockClassType'.
Line: 1187

Please find in all *.xml layout files string

class="\

and replace it with

class="

(Remove slash from the beginning of the class attribute value)

 

If you get this issue on the Magefan Blog post page, please do next:

1. Update blog extension to the min. v2.6.2
2. Check the file

app/design/frontend/ThemeVendor/themename/Magefan_Blog/layout/blog_post_view.xml

for the class="\ that is described above and make necessary modifications.