Netscape Communicator Datasheet (1997)

Layers were unique to Netscape 4.x (a.k.a “Communicator” vs. the older “Navigator” branding), so the Netscape ONE docs would probably be the best place to start if you can tolerate the fact that it's their tech so they're patting themselves on the back for it the entire time: https://web.archive.org/web/19990219125559fw_/http://develop...

Check out Chapter 2 “Dividing Content into Sections” in particular for examples: https://web.archive.org/web/20001207134400fw_/http://develop...

That chapter has a tantalizingly-broken link near the bottom: “For a comparison of CSS Positioning and positioning with the <LAYER> tag, see Danny Goodman's View Source article ‘CSS-Positioning — The Dynamic HTML Neutral Zone’”. I was able to fix the link (looks like it was MCom-intranet-formatted) and you can read it here: https://web.archive.org/web/19990129034353fw_/http://develop...

“Over and above this common [W3C CSS-Positioning (CSS-P)] standard, Netscape and Microsoft have applied these concepts to their own document object models and have developed different ways of conceptualizing these positionable entities. Netscape calls these items layers, and has even created a <LAYER> tag to facilitate adding such items into a document. Microsoft, on the other hand, refers to such items as styles. The challenge we scripters face is controlling Netscape's layers and Microsoft's styles to accomplish the same job.”

“Over and above this common standard” is particularly funny wording to me considering Microsoft are the ones with the reputation for embracing-and-extending but here Netscape are doing the same damn thing. It was already in their blood anyway considering we got the <IMG> tag from a similarly non-standard extension by Marc Andreessen when he was working on MCSA Mosaic, before MCom/Netscape: http://1997.webhistory.org/www.lists/www-talk.1993q1/0182.ht...

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For many years it was customary to have separate NS4 vs IE4 code paths by detecting the top-level objects that were unique to each browser, something like:

  if (document.layers) {
    // Netscape Communicator code
  } else if (document.all) {
    // IE code
  } else {
    // All other browser code
  }

Though my recollection is that `if NS4 else all-others-including-IE` was the most common pattern.