### All up-to-date significant adblockers¹

#### Element removal (a.k.a. cosmetic rules, a.k.a. hiding rules)
* `##.`: Hides parts of a page, based on one or more `class` values in the F12 filetree (separated with full-stops).
* `##`: Hides parts of a page based on the element type, e.g. `a`, `li`, `button`, `iframe`, etc., usually highlighted in purple in the F12 filetree.
* `###`: Hides parts of a page based on the `id` value.
* `#@#.`/`#@#`/`#@##`: Whitelists parts of a page to make them load.
* `[href="text"]`: Finds page elements whose values in the F12 filetree console contains such a value. The value can be `href`, `id`, `class`, `type`, or numerous other things. Does not support RegEx.
* `[href^="text"]`: Finds page elements whose value *begins* with the text.
* `[href$="text"]`: Finds page elements whose value *ends* with the text.
* `[href*="text"]`: Finds page elements whose value contains the text anywhere within it.
* `[href="text" i]`: Save as above, except case-insensitive.
* `:not(.element)`: Finds page elements that doesn't contain a specified element or text string. Can be paired with other syntaxes à la `:not(:-abp-contains(Example text))`.
* `:-abp-contains(text)`: Finds page elements that contains such text within it.
* `:-abp-has(.element)`: Finds page elements that contains such an element within it.
* `:nth-of-type(n)` / `:last-of-type` / `:only-of-type`: Finds page elements that are at a specific numerical position in a set.
* `:before` / `:after`: Removes the pseudo-elements that belong to a page element.
* `>`: Creates chain criteria, in which a selected page element must have a specific element above it in the filetree.
* `+`: Blocks the element that is right below the criteria in the filetree. Example: `##.element + div` blocks that particular `div`.

##### Advanced examples:
* The first two `##` of an element entry, are not used for elements written after e.g. `>`, `+` or `:-abp-has`. In those cases, the `##` in `##element` gets removed, `##.class` becomes `.class`, and `###id` becomes `#id`.
* `##element.element2`: Hide something both based on its element (##element1) and `class` value (.element2). Note the placement/absence of fullstops.
* While they're based on the same `class` values, `##.element1` will match any `class` (sub-)value, whereas `##div[class="element1"]` and their modifiers are based on the *entire* `class` string in the F12 filetree.
* `##.` / `##` / `###` entries can either be *generic*, in which they have no domains in front of them; or domain-specific, where they have one or more domains in front of them, separated by commas. Only Nano and uBO support wildcard asterisks (`*`) in such domains, while other adblockers do not.

#### File blocking (a.k.a. blocking rules)
* `||`: Blocks resources from domains or parts thereof from being loaded. For non-domain-specific resources, no pre-emption is needed at all.
* `@@`: Whitelists resources from specific URLs to make them load.
* `^`: Wildcard for anything that isn't alphanumerical or "_-.%" . Often used to cover both slash ( / ) and non-slash domain name endings at the same time.
* `$third-party`: Ensures that resources from a domain are only blocked if you're not visiting the domain itself.
* `$~third-party`: Ensures that resources from a domain are only blocked if you're visiting the domain itself.
* `$domain=`: Ensures that resources from a domain are only blocked if you're visiting a specified website. Multiple domains are separated with `|` (Vertical line) and not commas.
* `@@||` + `$generichide`: Prevents all non-domain-specific (a.k.a. generic) hiding entries from working on a website. On Nano/uBO it prevents *all* non-domain-specific entries from working.
* `@@||` + `$specifichide`: Prevents all domain-specific hiding entries from working on a website. On Nano/uBO it seems to prevent *all* domain-specific entries from working.
* `@@||` + `$elemhide`: Combines `$generichide` and `$specifichide`. Also completely breaks the element picker in Nano/uBO on that site as of the 14th of December 2019.
* `$script`: Blocks resources from domains or parts thereof from being loaded, but only if it's a script, e.g. a JavaScript runtime.
* `$csp`: Inserts additional *Content Security Policies* into the page.
* `$xmlhttprequest` / `$websocket` / `$dom`: Prevents such resources from being downloaded through the titular JavaScript APIs.
* `$popup` / `$image` / `$object` / `$font` / `$other`: These ones should hopefully be self-explanatory (Give me a heads-up in an issue report if it isn't).
* `$match-case`: Makes the criteria case-sensitive.
* `|text`: Matches URLs that *begin* with the text.
* `text|`: Matches URLs that *end* with the text.

#### Universal
* `! ` / `# `: Marks the start of a comment that shall not be interpreted as an entry.
* `~`: Means that an entry does *not* apply to a specific domain.
* `/\/\/\/` and similar: Text detections in RegEx format.
* `[Adblock Plus n.n]`: Used by Adblock Plus, AdBlock, and forks of them to determine if they should load the filterlist. Number is the intended minimum ABP version. `2.0` and `1.1` are most common; `3.1` and higher is on the rise and can be used to block support for old or low-quality forks. This has no effect on uBO or its forks.
* `! Title:` Specifies the intended name of the list. Required to make the name automatically show up in the settings of most adblockers, instead of the URL or of manual text input.
* `! Version:` The version number/alphanumeric of the list. Unofficially used to distinguish which version of a list a user is using. Used administratively by Adblock Plus' list report system (which requires a number-only version value). Many lists choose to use `! Last modified` as well or instead.
* `! Expires:`: Determines the timespan between each automated sync attempt with the list's source. Values are given in "n day/days". ABP also supports "hour/hours".

### Nano Adblocker, uBlock Origin, Adblock Plus and AdBlock only:
* `:scope`: Used alongside `:-abp-has` to make it only find elements whose criteria match their immediate subelements.

### Nano Adblocker, uBlock Origin and AdGuard only:
#### Hiding
* `:style`: Changes the CSS values of an element, in much the same way as what userstyle extensions like Stylish would've done.
* `{ }`: Same as above.
* `:has-text`: Same as `:-abp-contains`.
* `:has`: Same as `:-abp-has`.
* `!#if`: Specifies that a section of entries only applies to specific platforms or extensions. Closed out by `!#endif`.
* `:matches-css`: Looks for page elements whose existing native (i.e. non-inherited) CSS values match those of the criteria.
* `:matches-css-before`: Same as above, but looks for CSS values in its pseudo-elements instead.
* `$redirect`: Redirects resources to a neutered version that has been embedded in those extensions. Possible options are listed in [this file](https://github.com/gorhill/uBlock/blob/master/src/js/redirect-engine.js) (AdGuard has a [slightly smaller selection](https://github.com/AdguardTeam/AdguardBrowserExtension/blob/master/Extension/lib/filter/rules/scriptlets/redirects.yml)).
#### Blocking
* `$badfilter`: Deactivates a resource-blocking entry, even if it is present in another list.
* `$important`: Makes a resource-blocking entry take precedence over another whitelisting entry.

### Nano Adblocker and uBlock Origin only:
#### Hiding
* `!#include`: Embeds another filterlist that is hosted on the same domain (with numerous restrictions).
* `##+js` (prev. `##script:inject`): Invokes a script that is embedded in those extensions, and usually using the script to modify a value on the site. Possible options are listed in [this file](https://github.com/gorhill/uBlock/blob/master/assets/resources/scriptlets.js) (The top strings of each paragraph). Nano has a select few additional scripts.
* `:xpath`: An entry written with the very advanced Xpath syntax.
* `##^`: Blocks resources before they've even been loaded, based on their values in *View source* instead of their F12 ones.
* `:nth-ancestor`: Looks for elements that are a certain amount of indentations (i.e. filetree floors) above the criteria in the F12 filetree.
#### Blocking
* `127.0.0.1` / `0.0.0.0` / `::1` / `0` / `::`: Used by "*hosts*" system files to signify that network requests to such a domain shall be redirected to a local-only IP address, thus preventing it from loading. Nano and uBO treats it the same as `||`. It only supports whole domains; using `/` or any other non-alphanumeric-or-period characters is not accepted.
* `||` + `$document`: Guarantees a danger warning when loading a page, which is not 110% guaranteed otherwise.
* `$3p`: Same as `$third-party`.
* `$1p` / `$first-party`: Same as `$~third-party`.
* `$xhr`: Same as `$xmlhttprequest`.
* `$all`: Officially combines all other non-party `$` values. In practice it combines the use of no `$` values at all + `$popup`.

### Adblock Plus and AdBlock only:

* `! Redirect: `: Tells the adblocker to look for list updates from a new URL from that point on.
* `#?#`: Required to make entries with `:-abp-has`, `:-abp-contains` and `:-abp-properties` work in those particular extensions, and to make `:style` entries not break the list extremely heavily.
* `@@||` + `$document`: Turns off adblocking entirely while on that domain.
* `@@||` + `$genericblock`: Prevents all non-domain-specific blocking entries from working on a website.
* `:-abp-properties`: A highly modified version of `:matches-css[-before]`, with some syntax differences. Can also select text encodings (à la Base64) and a few other non-CSS traits.
* `$rewrite=abp-resource:`: Similar to `$redirect`, but with a rather different selection of neutered files. Possible options are listed on [this help page](https://help.eyeo.com/adblockplus/how-to-write-filters#rewrite).
* `#$#`: Similar to, but incompatible with, `##+js`. Possible options are listed in [this file](https://gitlab.com/eyeo/adblockplus/adblockpluscore/blob/next/lib/content/snippets.js) (text-search `@alias`).

### AdGuard only:

* `#%#//scriptlet`: Similar to, but only partially compatible with, `##+js` and ABP's `#$#`. Possible options are listed in [this file](https://github.com/AdguardTeam/AdguardBrowserExtension/blob/master/Extension/lib/filter/rules/scriptlets/scriptlets.js) (text-search ".names").
* `#%#AG_`: A few extra scriptlets for whom documentation appears to be non-existent.
* `#%#` without `//scriptlet`: Appears to insert JavaScript code that is written into the list, as opposed to from an embedded file.
* `$empty`: Results in a fake empty page being loaded, instead of an error page.
* `:properties`: Claims to be similar to `:-abp-properties`, but is incompatible with it.
* `$$script`: Uses very advanced criteria to block scripts that meet them.
* `$cookie`: Blocks cookies.
* `$cookie=`: Blocks cookies with specific names.
* `$cookie=` + `maxAge`: Changes the cookie to have an expiration time in seconds.
* `$cookie=` + `same-site`: Changes the cookie to use the "Lax" mode of `samesite` known from the `Set-Cookie` browser HTTP response system.
* `$mp4`: Seems to be equivalent to `$redirect=noopmp4`, but does not require any AdGuard trust rights. Allegedly to be obsoleted soon.

### AdGuard for [Windows/Mac/Android] only:

* `! Description:`: Shows a description of the list's purpose, when the question mark next to the list in the AdGuard settings is hovered over. That being said, a description is convenient for users of all adblockers, if they're willing to look up a list's raw content.
* `$network`: When applied to an IP address, it blocks all incoming requests from it, and not just when it's typed into a browser address bar. Individual ports can be specified with `:`. IPv6 addresses must be surrounded by square brackets. Can very easily break legitimate sites as collateral damage, and should be used very sparingly.
* `@@` + `$jsinject`: Prevents `#%#` entries from working on that site.
* `@@` + `$extensions`: Prevents AdGuard userscripts from working on that site.
* `@@` + `$content`: Prevents `$$script` entries from working on that site.
* `@@` + `$stealth`: Turns off Stealth Mode on that site.
* `$replace`: Changes the text of text elements on a site. Supports and requires use of RegEx. Requires ridiculous amounts of trust rights and cannot be used in web-hosted lists.

# Other particularly important usage notes

* To make the text detection for `:-abp-contains` and `:has-text` case-insensitive, wrap the paranthesised text into `(/Example text/i)`.
* The `"` in `[href="text"]` is optional, but *only* if the criteria text is only a single word and has no numbers.
* `:style` and `{ }` does not allow changing `background-image` into a URL value.
* It is claimed in [this comment](https://github.com/DandelionSprout/adfilt/issues/7#issuecomment-481978609) that Safari does not properly accept the use of `$third-party`.
* Amazingly, using `! Redirect: ` in the intended target link's list, will cause an infinite loop that prevents the list from being loaded.
* In Opera, the F12 filetree is not actually opened with F12 by default, but instead with Ctrl+Shift+I (Capital İ).

¹ = Includes Nano Adblocker, uBlock Origin ≥1.20.0, AdGuard, AdNauseum, Adblock Plus version ≥3.5, and AdBlock. It does **not** include AdGuard Home, Brave Browser, Slimjet, uBlock non-Origin, Tracking Protection List, or Blokada, whose syntax supports are considerably inferior to the above list.