•Allow spaces around '=' when assigning an attribute value - Check this box if you want HTML Validator to not generate warning messages for attributes that have spaces before or after the equals sign. For example, if this box is not checked, align = center and align= center will generate warning messages due to the spaces around the equals sign. If this box is checked, spaces around the equals sign do not generate validation warnings. According to HTML 4.0, spaces are valid around '=' when assigning values to attributes. This option is enabled by default.
•Allow multi-line quoted strings - Check this box if you want to be able to split attribute value quoted strings on more than one line, otherwise a warning message is generated. It is usually best to keep this box unchecked and to keep quoted attribute value strings on a single line. This makes it easier to find errors when an opening or closing quotation mark is missing, which often causes numerous other errors to be generated. It is also possible that having a quoted attribute value string that is broken up onto two or more lines may cause problems or confusion with some browsers. This option is not enabled by default.
NOTE: CSS HTML Validator tries to suppress the message if the newline is in a data URI like src="data:...". (New v12.0027)
NOTE: CSS HTML Validator suppresses the message if it's in foreign content, like SVG. (New v17.0100)
•Treat single and double quotes as equivalent - Check this box if you want HTML Validator to treat single and double quotes as equivalent when they are used to enclose attribute values. This function will cause an attribute value that is enclosed in single quotes not to generate an error message if the configuration requires that the value must be enclosed in double quotes, because the single quotes are 'equivalent' to the double quotes. You should keep this option enabled if your documents are written for 'modern' browsers that should not have problems with using single quotes. This option is enabled by default.
•Require all attribute values to be quoted - Check this box if you want HTML Validator to require that all attribute values be in quotation marks. This option is not enabled by default.
•Require attribute values for all attributes - Check this box to require that ALL attribute names have attribute values. This option should be checked for XML or XHTML style documents. The default configuration file that is included with HTML Validator will automatically enable this option if an XHTML document is detected. This option is not enabled by default.
•Ignore quotation requirements for attribute values - Check this box if you want HTML Validator to ignore all quotation requirements for attribute values. HTML Validator will not generate error messages due to quoting or failing to quote any attribute values. We recommended that you keep this option unchecked. This option is not enabled by default.
•Ignore attributes with colons in their name - Check this box to ignore attributes with colons (:) in their name if there is no attribute with the same name in the configuration. If checked and there are attributes that have been ignored due to this option, then a message will be generated with the number of attributes ignored. In v12.0112+, this option does not apply to names beginning or ending with a colon, or beginning with "data-". This option is enabled by default. (New v9.00)
•Warn about missing attributes for attributes with "Warn if missing" option set - Check this box if you want HTML Validator to generate warning messages for missing attributes that have the Warn if missing option checked in the attribute's configuration (this option is set in the Attributes Editor of the Configuration Editor). This option is enabled by default.