1. CSS Flexible Box Layout Module

    Method of positioning elements in horizontal or vertical stacks. Support includes all properties prefixed with `flex`, as well as `display: flex`, `display: inline-flex`, `align-content`, `align-items`, `align-self`, `justify-content` and `order`.

  2. Context menu item (menuitem element)

    Method of defining a context menu item, now deprecated and [removed from the HTML specification](https://github.com/whatwg/html/issues/2730).

  3. clipboarditem api

  4. clipboarditem api: types

  5. cssrulelist api: item

  6. cssstyledeclaration api: item

  7. cssvaluelist api: item

  8. datatransfer api: items

  9. domrectlist api: item

  10. domstringlist api: item

  11. domtokenlist api: item

  12. filelist api: item

  13. htmlallcollection api: item

  14. htmlcollection api: item

  15. htmlselectelement api: item

  16. medialist api: item

  17. mimetypearray api: item

  18. namednodemap api: item

  19. nodelist api: item

  20. pluginarray api: item

  21. plugin api: item

  22. speechgrammarlist api: item

  23. speechrecognitionresultlist api: item

  24. speechrecognitionresult api: item

  25. stylesheetlist api: item

  26. touchlist api: item

  27. css at-rule: `@font-face`: src: drop invalid item (not src string)

  28. css property: align-items

  29. css property: align-items: `anchor-center`

  30. css property: align-items: supported in flex layout

  31. css property: align-items: supported in flex layout: `baseline`

  32. css property: align-items: supported in flex layout: `first baseline`

  33. css property: align-items: supported in flex layout: `last baseline`

  34. css property: align-items: supported in flex layout: `safe` and `unsafe`

  35. css property: align-items: supported in flex layout: `start` and `end`

  36. css property: align-items: supported in grid layout

  37. css property: align-items: supported in grid layout: `start` and `end`

  38. css property: counter-increment: list-item

  39. css property: counter-reset: list-item

  40. css property: counter-set: list-item

  41. css property: display: list-item

  42. css property: display: list-item: supported on `<legend>`

  43. css property: justify-items

  44. css property: justify-items: `anchor-center`

  45. css property: justify-items: supported in flex layout

  46. css property: justify-items: supported in grid layout

  47. css property: place-items

  48. css property: place-items: supported in flex layout

  49. css property: place-items: supported in grid layout

  50. html element: summary: `display: list-item`