Sticky Start Threshold

Compute the simple sticky-start scroll threshold from independently measured normal position and inset; containing-block end constraints are outside scope.

Description

Compute the simple sticky-start scroll threshold from independently measured normal position and inset; containing-block end constraints are outside scope.

A simplified sticky-start threshold is the normal position minus the desired sticky inset.

When to use this tool

Compute the simple sticky-start scroll threshold from independently measured normal position and inset; containing-block end constraints are outside scope.

Prepare the supplied normalStart, stickyInset fields for this operation.
Compare the complete example with the representation used by your own input before carrying the result into another step.

How to use the tool and how it works

Enter normalStart, stickyInset. Use the exact text syntax, units and index conventions explained below.
Run the tool. If input validation fails, correct the supplied fields before interpreting any result.
Read result.scrollThreshold. Interpret false, null and empty lists using the distinctions below; they can be valid outputs.

Return normalStart-stickyInset as scrollThreshold using the supplied finite coordinates.^[1]

Input field	Meaning and representation	Accepted input
normalStart	normal start.	Finite number
stickyInset	sticky inset.	Finite number

Output field	Interpretation
result	Object containing the named outputs below.
result.scrollThreshold	The scroll threshold value under the stated formula or text convention.

json

{
  "input": {
    "normalStart": 100,
    "stickyInset": 10
  },
  "output": {
    "result": {
      "scrollThreshold": 90
    }
  }
}

Limitations and assumptions

This is arithmetic only, without a containing block, sticky end constraint, writing mode or browser layout engine.
Rectangle arrays use [x,y,width,height] with nonnegative extents. All dimensions must use the same coordinate frame and unit; values are supplied rather than measured from a page.
Every declared top-level field is required and unexpected fields are rejected. Numeric inputs must be finite; ordinary text fields are bounded to 8,192 UTF-16 code units, with tighter operation-specific limits where stated.
String lists have at most 128 entries of at most 128 code units; matrices have at most 128 rows and columns. Larger numeric lists and parsed JSON have separate bounded budgets. Nonfinite results and excessively large serialized outputs are rejected.
Indexes are zero-based and spans have an exclusive end unless explicitly stated otherwise. A valid false, null or empty-list result is distinct from malformed input.

Alternative or Complementary methods

Measure the actual layout when browser behavior matters. The formulas use supplied coordinates and explicit simplifications; they do not account for every box, writing mode, clipping ancestor or simultaneous layout change.

References

Tool behavior and example: Sticky Start Threshold — tool.io

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