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Module Tree.Collapsible_margin_setSource

Collapsible margin tracking for CSS Block layout.

In CSS Block layout, adjacent vertical margins collapse according to specific rules. This module tracks sets of collapsible margins during layout computation, maintaining the largest positive and smallest (most negative) margins encountered. The final collapsed margin is the sum of these two values.

Margin Collapsing

CSS specifies that vertical margins between adjacent block-level boxes collapse. When multiple margins collapse together, the resulting margin is:

  • For positive margins: the maximum of all positive margins
  • For negative margins: the minimum (most negative) of all negative margins
  • Final collapsed value: positive + negative

This implements the margin collapsing semantics defined in CSS 2.1 Section 8.3.1.

Usage

Create a margin set from a single margin:

  let margin_set = Collapsible_margin_set.from_margin 16.0

Collapse additional margins into the set:

  let collapsed =
    margin_set
    |> Collapsible_margin_set.collapse_with_margin 24.0
    |> Collapsible_margin_set.collapse_with_margin (-8.0)

Resolve the final collapsed margin:

  let final_margin = Collapsible_margin_set.resolve collapsed
  (* = 24.0 + (-8.0) = 16.0 *)
Sourcetype t = {
  1. positive : float;
  2. negative : float;
}

The type representing a set of collapsible margins.

Maintains the largest positive margin and the smallest (most negative) margin encountered during margin collapsing.

Sourceval zero : t

zero is a margin set with no collapsible margins.

Both positive and negative are 0.0.

Sourceval from_margin : float -> t

from_margin margin creates a margin set from a single margin value.

If margin >= 0.0, sets positive = margin and negative = 0.0. Otherwise, sets positive = 0.0 and negative = margin.

Sourceval collapse_with_margin : t -> float -> t

collapse_with_margin t margin collapses margin into margin set t.

Returns a new margin set where positive is max t.positive margin if margin >= 0.0, or negative is min t.negative margin if margin < 0.0. The other field remains unchanged.

Sourceval collapse_with_set : t -> t -> t

collapse_with_set t other collapses margin set other into t.

Returns a new margin set with positive = max t.positive other.positive and negative = min t.negative other.negative.

Sourceval resolve : t -> float

resolve t computes the final collapsed margin value.

Returns t.positive + t.negative. This is the effective margin after all collapsing rules have been applied.

Sourceval to_string : t -> string

to_string t returns a debug string representation of the margin set.

Sourceval compare : t -> t -> int

compare a b provides total ordering for margin sets.

Compares first by positive, then by negative if positive values are equal.

Sourceval equal : t -> t -> bool

equal a b tests structural equality of two margin sets.

Returns true if both positive and negative fields are equal using Float.equal.

Sourceval pp : Format.formatter -> t -> unit

pp fmt t is a pretty-printer for margin sets.