Validation errors are considered identified during verification web page code inconsistencies to generally established standards that can affect the correctness of work and the display of individual elements or the entire site as a whole.

Frequent validation errors include:

  • lack of the Doctype tag that is needed to browser could correctly determine the type of document he downloads;
  • problems with the conversion of special characters;
  • use of block elements inside lowercase;
  • uncovered elements (deposit violation), the wrong number of quotation marks;
  • no attribute alt those present on the page of images;
  • HTML-element in the wrong section;
  • lack of required tags in the structure of elements;
  • tags that must be in single form within a separate web page are repeated several times.

Not all validation errors are critical and require correction. A properly working site when checking the validity of the code may well receive a dozen or two comments, the presence of which is quite acceptable if they do not affect its display and level usability.