is_404() – where does this get set?

There is a dedicated method for it WP_Query->set_404(). From quick search through code it can be set in WP_Query->parse_query() or WP->handle_404() (note WP, not WP_Query!).

But it can (and sometimes does) get set on query externally, for example by plugin that needs to invalidate specific resource.

Related Posts:

  1. Why is the loop not empty on some 404s?
  2. How to trigger 404 for custom query var?
  3. Pagination shows 404 after a certain number of pages
  4. Pagination causes error 404 when used with front-page.php
  5. WP-PageNavi gives me a 404 when using WP Query
  6. Intentionally exceed max_num_pages on main query without getting 404?
  7. Custom pagination with WP_Query generating 404 error
  8. if/else on custom query gives 200 OK when condition not met?
  9. Have functions work outside the loop with 404 override
  10. How to return a 404 when custom query matches nothing?
  11. paged variable not working for category/custom post archive
  12. Issue with front page navigation after upgrading to 3.4
  13. Show a 404 error page if Public query variable’s value doesn’t exist?
  14. How to use if($wp_query->query_vars[‘name’] == ‘pagethatdontexist’) without getting a 404? How to suppress 404
  15. Custom Taxonomy Breaks Pages
  16. Reciving Error 404 blog/page/2/
  17. Show a message if there are no active posts in category
  18. Pagination with Custom Post Type not working on index.php: I get a 404
  19. taxonomy-{term}.php terms pagination returning 404 after a certain page
  20. PHP memory friendly alternative to get_posts()
  21. Sorting posts by custom date fields (non standard date format)
  22. How to filter sql only for a specific post type
  23. Loop with break in the middle
  24. What should I use, get_posts or wp_query for less CPU load?
  25. How should I use posts_where to change meta_value from a string to integer?
  26. Reduce Database Queries in Code [duplicate]
  27. meta_query with array as value
  28. Sort in WP_Query(), not filter? Is it possible?
  29. Determine WP_Query parameters from URL
  30. wordpress query in header won’t reset and corrupts other loops
  31. How add a custom posttype name using ACF field to a query post array
  32. Php Trying to get property ‘ID’ of non-object
  33. More than 1 Year Date Query
  34. Is it possible to dynamically get queried term AND taxonomy?
  35. posts_per_page not working
  36. Pull post meta with post_query?
  37. How do I force WP_query to fetch fresh, non-cached results?
  38. Complex WP_Query (two post types and multiple operators)
  39. Five posts from a category in footer
  40. Remove category from query (show all posts in archive.php) pre_get_posts()
  41. How to Union two different conditions in one WP_Query
  42. Display filtered results into custom page
  43. WooCommerce – get product sub categories
  44. Order by empty custom field
  45. WP_Delete_user link creation
  46. How to exclude post formats from wordpress recent posts in a tabs widget [closed]
  47. How to pass orderby params to $wpdb->prepare()?
  48. how update data through ajax and jquery
  49. WP_Query arguments relation shows AND instead of OR
  50. Combine results of multiple WP_Query to resemble single WP_Query
  51. Using WP_Query() in Magento shows error
  52. For what queries is conditional tags informative?
  53. Utilising an existing page while using the “s” query parameter
  54. posts archive page – closing WP_Query loop correctly [closed]
  55. AJAX Breaking Offset Argument In WP Query
  56. Get meta_value of a specific meta_key from all posts belonging to a specific custom type
  57. Excluding posts with certain value of meta_key keeping posts without that meta_key
  58. Pagination in html table is not working
  59. Nested array issue in meta_query
  60. WP_query problem -spurious results
  61. Avoid duplicate while merging two query post
  62. Query Not working as expected
  63. How to create single page site in WordPress
  64. Widgets: Show Recent Posts Only if the Posts Have Both Categories X and Y
  65. Execute PHP function inside the admin area
  66. Populate select list with meta values from all posts of a Custom Post Type
  67. tax_query not working on custom post type
  68. WordPress Meta Query Null Values Order
  69. WooCommerce WP_Query using tax_query returns no results (0 = 1)
  70. WP Query and multiple queries
  71. I need query_posts() to order results first by a meta value and then by post ID
  72. Custom category page with taxonomy filters
  73. How do i query woocommerce booking post type on init action?
  74. make query more simplest and in one query
  75. How to display post based on which is clicked
  76. date_query problem
  77. WP_Query Not Working with Variable
  78. WP_Query doesn’t return some child pages even though the database shows them
  79. How to allow Readers to Select Post Order?
  80. Random posts in WP_Query when searching by tag
  81. How To Use WP_Query To Get The Custom Post type Posts With Keywords
  82. Pagination returns 404 after page 20
  83. 423 queries in 6.098 seconds
  84. I wan to process the following js to process the AJAX Request on my function to calculate author Total Post views
  85. (How) Can I use ‘wild cards’ on the left hand side of an array argument?
  86. ‘s’ term in WP_Query extended class causes huge memory leak (268MB)
  87. Compare meta key separation
  88. Combine privileged users array with my current query
  89. Get posts from similar time as current post
  90. Query posts filter not working
  91. meta_query dates from an array
  92. Creating array to compare custom field values
  93. WordPress Query Default Order if Meta Values Same?
  94. WP_Query do not include posts with a certain value in a custom field –
  95. Having trouble using this post category query on multiple pages?
  96. Remove 5 latest posts from the loop
  97. Exclude post formats in custom loop
  98. WordPress WP_User_Query ignores the `meta_query` when called from an Ajax function
  99. Unexpected results custom wp_query and $the_query->request;
  100. Simple Apex Charts with jQuery not working
tech