The Perplexing Nature of Flex Items: Block or Flex Level?

The question of whether flex items are block level has been a topic of debate among CSS developers. The CSS Flexible Box Layout Module Level 1 states that flex items are at the flex level and not at the block level. However, a later section suggests that flex items' display values are "blockified." This raises the question: are flex items block level after all?

To understand the discrepancy, it's crucial to understand the concept of display in CSS. Each element has a display property that defines how it is laid out. For flex items, the display value is initially set to "block." This means that if a flex item's inline property is set to another value, such as inline-block, it will be automatically converted to block. This is known as blockification.

Therefore, while flex items are inherently considered flex-level boxes, their display value is blockified. This does not make them block-level boxes in the traditional sense. They remain flex-level boxes but behave like block elements from within their own formatting context.

To sum it up, flex items exist at the flex level, but their display value is blockified. This distinction allows them to participate in flex formatting while also acting as block elements for their contained elements. Understanding this concept is crucial for accurate CSS layout and styling.