The GG Network blog — page 18

A disallowed URL can still show up in search results, and the noindex tag that would keep it out only works if the crawler is allowed to fetch the page.

A 301 gets cached by browsers, sometimes with no expiry, and undoing one means reaching machines you do not control. Also: why two hops usually means one too many.

It is one integer: seconds since 1970 in UTC. Every time-zone bug and every accidental trip to the year 57971 comes from what happens after that.

Luhn is a checksum for catching typos. It says a string of digits is internally consistent — not that an account exists, and not that anyone owns it.

The first digit of an HTTP status tells you whose problem it is. The pairs that get confused — 401 against 403, 301 against 302 — are where the debugging time goes.

A diff is supposed to find the smallest set of changes between two texts. Line endings, trailing spaces and one inserted line are the three things that bury the real one.

The same string needs three different treatments in a path, a query value and a form body. Here is one string escaped all three ways, with the reasoning.

Why the four characters that break markup have to be escaped before user text reaches a page, and why escaping for text and for an attribute are not the same job.

A query string is text with conventions, not a data structure. Here is what ?a=1&a=2 means, why frameworks disagree, and why splitting before decoding is the one order that works.

What padding is for, what a decoder will and will not accept, and why decoded content is still untrusted input that has to be escaped for wherever it lands.

A diagonal measurement tells you almost nothing about how much surface you get, because the answer depends on the shape as well as the length. The formula, worked through at one fixed diagonal.

Pixels per inch comes from Pythagoras on the pixel grid, and it is exact arithmetic. What it cannot do on its own is describe what reaches a viewer, because that depends on distance.