Flexbox: "The specification describes a CSS box model optimized for user interface design. In the flex layout model, the children of a flex container can be laid out in any direction, and can “flex” their sizes, either growing to fill unused space or shrinking to avoid overflowing the parent. Both horizontal and vertical alignment of the children can be easily manipulated. Nesting of these boxes (horizontal inside vertical, or vertical inside horizontal) can be used to build layouts in two dimensions."
They just re-invented HTML tables.
The replacement of HTML tables for layout with "float" and "clear" was a disaster. It replaced a 2D model with a 1D model. There were years of Javascript hacks to deal with that. Now, the 2D model of tables is back, but with a new name, because the cool kids won't use tables.
As someone who has implemented tables in a browser engine, the idea that flexbox layout just duplicates table layout is completely untrue. Tables are extremely complex, don't have a complete specification, and differ between browsers.
Just to give one example, the algorithm for computing widths of table columns involves creating four "candidate guesses" of all the column widths using different algorithms for each, selecting the two guesses that most closely bound the available width, and then linearly interpolating between them [1]. And that's the easy case, when there are no colspans: when you get colspans, the layout parameters are defined by a complex recursive series [2]. Flexbox has none of this complexity: it basically does the simple thing you'd expect.
They just re-invented HTML tables.
The replacement of HTML tables for layout with "float" and "clear" was a disaster. It replaced a 2D model with a 1D model. There were years of Javascript hacks to deal with that. Now, the 2D model of tables is back, but with a new name, because the cool kids won't use tables.