HTML Class Token Stable Merge

Merge explicit HTML class attribute strings as stable exact token union after ASCII whitespace tokenization; preserve first token appearance.

Description

Merge explicit HTML class attribute strings as stable exact token union after ASCII whitespace tokenization; preserve first token appearance.

Class strings from several sources can be merged without reordering the first appearance of a class name. This produces a stable token union.

When to use this tool

Merge explicit HTML class attribute strings as stable exact token union after ASCII whitespace tokenization; preserve first token appearance.

Prepare the supplied classLists 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 classLists. 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.classes. Interpret false, null and empty lists using the distinctions below; they can be valid outputs.

Tokenize each classLists string on HTML ASCII whitespace, concatenate in list order, keep the first occurrence of each exact token and join with single spaces.^[1]

Input field	Meaning and representation	Accepted input
classLists	class lists.	List of strings; at most 128 entries

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

json

{
  "input": {
    "classLists": [
      "a b",
      "b\tc"
    ]
  },
  "output": {
    "result": {
      "classes": "a b c"
    }
  }
}

Limitations and assumptions

This merges names only. It does not resolve competing CSS rules, interpret selectors or normalize case.
All declared input fields are required and unexpected top-level fields are rejected. Numbers must be finite; lists are limited to 128 entries and ordinary text fields to 8,192 UTF-16 code units, with tighter limits where stated.
JSON text inputs must parse within bounded nesting and size limits. Numeric outputs outside the safe finite range are rejected; large exact integer results use decimal strings. Indexes and half-open spans are zero-based unless a rank is explicitly described as one-based.

Alternative or Complementary methods

For actual document behavior, inspect a parsed DOM and the relevant HTML algorithm. These tools transform supplied tokens, observations or coordinates; compare the browser result when parsing or layout matters.

References

Tool behavior and example: HTML Class Token Stable Merge — tool.io

Similar or alternative tools

HTML Class Token Difference
Subtract literal HTML class tokens while preserving surviving duplicates and order; CSS selector syntax and case folding are not applied.
HTML Class Token Duplicate Audit
Audit class token duplicates using HTML ASCII whitespace splitting and exact case-sensitive token identity; does not parse selectors or CSS escapes.