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troubleshooting

If you use 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

You need to check all layout files in your theme and custom extensions, they may have a code e.g.:

class="\Magento

you need to change it to

class="Magento

and then flush the Magento cache.

In order to find all bad layout files you can run the CLI command in Magento 2 root directory:

grep -r app -e 'class="\\'

Note that most likely you get this error because of using outdated versions of Magento 2 extensions or themes.