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CSS parsing issues

Parsing issues independent of CSS specification

Code
Summary
Details
Missing end of comment
A CSS comment was found, but the end of the comment was missing.
Closing quote is missing
An opening quote was found, but the matching end quote was missing. Outside of strings, quotes must always appears in matching pairs, and any single quotes must be escaped using '\'.
Closing brace '}' is missing
The start of a block '{' was found, but the matching end brace '}' was missing.
Mismatched pairs of '()', or '[]' found
Outside of strings, you must have matching pairs of parentheses '()' and square brackets '[]'. This error is normally displayed when there is a missing parenthesis or bracket, or an additional one has been entered by mistake, or an extra one has been deliberately added but hasn't been properly escaped using '\'.
An incomplete at-rule has been detected
The start of an at-rule was found, but the rest of the rule appears to be missing.
A block was expected but was not found
A block was expected but the opening brace '{' at the start of a block could not be found.
A selector was expected but could not be found
A selector appears to be missing. This may be caused by the complete absence of any selector, or in a complex selector one of the simple selectors is missing. This may be due to a simple error such as having an extra comma.
The block appears to have ended prematurely
The closing brace '}' of a block appears before the end of the declaration.
The property name is missing
A property name was expected but could not be found.
Incomplete declaration
The declaration appears to be incomplete. Either no property name or no values were found.
The semi-colon is missing from the end of the at-rule
at-rules should either have a block or a statement ending with a semi-colon, and in this case neither could be found.
The identifier includes a character which is not allowed
Identifiers are restricted in the characters that are allowed. Note that there are normally greater restrictions on the first character of the identifier compared to the rest of it. See "https://www.w3.org/TR/CSS2/syndata.html#characters (displayed in new window).

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CSS non-conformance

Issues due to non-conformance with the chosen CSS specification

Code
Summary
Details
Unknown at-rule
The at-rule is not recognised as valid for the CSS Level used for the validation.
The @charset rule is not allowed here
The @charset rule can only be used in a separate CSS document and not in HTML documents.
The @charset rule must be the first line in the document
The exact 10 characters @charset " must be the first thing in the document. Anything, even white space, prior to this will trigger this error. See https://www.w3.org/TR/CSS2/syndata.html#charset (displayed in new window).
The character set is not recognised
The character set specified is not recognised. This may be because it is misspelled.
The @import rule does not precede all other rules
Any @import rules must precede all other rules, except the @charset rule. See https://www.w3.org/TR/CSS2/cascade.html#at-import (displayed in new window).
The at-rule used is not formatted correctly
The at-rule used does not follow the accepted format for this rule.Please consult the relevant documentation for details.
Invalid characters found in URI
URIs can only contain a limited set of characters. See https://www.ietf.org/rfc/rfc2396.txt (displayed in new window).
An item is not allowed here
An at-rule, property or other item was used which is not allowed in this context.
Invalid @page selector used
The @page rule can only be used with a restricted number of selectors. In this case the selector used was not recognised as valid for the @page rule.
Missing font family
With the @font-feature-values rule, one or more font family names should be provided.
One or more of the listed font families is badly formatted
One or more of the font family names listed do not meet the requirements of the specification.
Missing feature value list
With font variant value definitions, a list of feature values must be provided.
Invalid feature value list
The list of feature values does not meet the requirements of the specification.
One or more required font descriptors are missing
The @font-face at-rule must have both a 'font-family' and a 'src' descriptor.
The @namespace rule does not precede all other rules
Any @namespace rules must precede all other rules, except the @charset and @import rules. See https://www.w3.org/TR/css3-namespace/#syntax (displayed in new window).
The namespace NAMESPACE has not been not declared
A @namespace rule declaring the namespace used in the selector was not found.
A counter-style type descriptor is required
MISSING_FEATURE_VALUE_LIST
The counter-style name has an invalid name
The @counter-style at-rule cannot have any of these names: 'disc', 'decimal', 'default', 'unset', 'inherit', 'initial', 'revert' or 'none'.
The @charset rule is badly-formed
@charset must be written literally; the 10 characters @charset \" (lowercase, no backslash escapes), followed by the encoding name, and ending with \"; See https://www.w3.org/TR/CSS2/syndata.html#charset (displayed in new window).
Missing or invalid palette name
With the @font-palette-values at-rule, a valid author-defined palette name must be provided.
A font-family descriptor is required
The @font-palette-values at-rule must have a 'font-family' descriptor.
Pseudo-elements can only appear at the end of a selector
Pseudo-elements may only be appended after the last simple selector of the selector. See https://www.w3.org/TR/CSS2/selector.html#pseudo-elements (displayed in new window).
The pseudo-element/pseudo-class used was not recognised
Each CSS standard allows different pseudo-elements and pseudo-classes to be used, and one used here does not match the list of allowed pseudo-classes/pseudo-elements for this CSS Level.
A media type is missing
A media type was expected but appears to be missing. This can be caused by an extra comma in a list of media types.
The media type MEDIA_TYPE was not recognised
Each CSS standard allows different media types to be used, and the type used here does not match the list of allowed types for this CSS Level.
A media query contains a parsing error
The media query contains a colon (:) in the wrong place.
Unknown media feature: MEDIA_FEATURE
The media feature name is not recognised as valid for the CSS Level used for the validation.
TEXT_DESCRIBING_PROBLEM: RULES_FOR_THIS_FEATURE
The value used is invalid for this media feature, because the value does not follow the allowed rules for this feature. A list of valid rules will be displayed for the feature.
The 'to' and 'from' keywords must appear only once
The 'to' and 'from' keywords must appear only once in a keyframe selector. See https://www.w3.org/TR/css-animations-1/#keyframes (displayed in new window).
Invalid percentage found in keyframe selector
Percentages must contain the '%' character and the value must be between 0% and 100%. See https://www.w3.org/TR/css-animations-1/#keyframes (displayed in new window).
Unknown property: PROPERTY_NAME
The property name is not recognised as a valid name for the CSS Level used for the validation.
TEXT_DESCRIBING_PROBLEM: RULES_FOR_THIS_PROPERTY
The value used is invalid for this property, because the value does not follow the allowed rules for this property. A list of valid rules will be displayed for the property using the format used in the chosen standard.
TEXT_DESCRIBING_PROBLEM: RULES_FOR_THIS_DESCRIPTOR
The value used is invalid for this descriptor, because the value does not follow the allowed rules for this descriptor. A list of valid rules will be displayed for the descriptor using the format used in the chosen standard.
The '!important' keyword is not allowed here
The '!important' keyword is only allowed in property values and not in declaration values.
A vendor extension has been used
Authors should avoid using vendor extensions where possible. See https://www.w3.org/TR/CSS2/syndata.html#vendor-keywords (displayed in new window).

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