Alpha
Opacity

	Alpha values are real numbers in the closed interval from 0 to 1,
	where 0 means full transparency, and 1 means full opacity.

Blend Mode

	Blend modes define how a layer of graphics combines with a backdrop.

	Below is an illustration of the visual effect for RGB colors for the blend
	modes defined for PDF.

	For further details refer to the PDF specification's `section
	on blend modes
	<https://opensource.adobe.com/dc-acrobat-sdk-docs/pdfstandards/pdfreference1.7old.pdf#G12.12449365>`_.

	.. imagesvg:: ../../images/blendmodes.svg
		:tagtype: object
		:width: 75%

File specification

	In PDF a file specification names a file.

	If a file specification only contains a file name or a path,
	then it represents an external file. Such a file is assumed
	to be found at the specified location in the file system.

	A file specification may also embed the file contents as a
	stream inside the PDF. In this case the file specification
	represents an embedded file. For embedded files, further
	metadata may be stored (e.g. file size, creation and
	modification date).

	For more details read the PDF specification's section on
	`file specifications
	<https://opensource.adobe.com/dc-acrobat-sdk-docs/pdfstandards/pdfreference1.7old.pdf#G8.1640832>`_.

Knockout and Isolation

	In a knockout transparency group each element overwrites the prior
	elements in the group instead of compositing with them.

	In an isolated transparency group the group does not composite with
	the group's backdrop, but rather a fully transparent backdrop.

	For further details refer to the PDF specification's sections on
	`isolation <https://opensource.adobe.com/dc-acrobat-sdk-docs/pdfstandards/pdfreference1.7old.pdf#G12.1689467>`_
	and
	`knockout <https://opensource.adobe.com/dc-acrobat-sdk-docs/pdfstandards/pdfreference1.7old.pdf#G12.1689478>`_.

	.. imagesvg:: ../../images/knockout-isolated.svg
		:tagtype: object
		:width: 75%

Winding
Non-zero Winding Number Rule
Even-Odd Rule

	These rules in PDF defined what parts of a `Path` are inside and
	outside the curve respectively. This is used to determine what parts
	of a curve should be filled.

	See the PDF specification sections on the
	`Non-zero Winding Number Rule <https://opensource.adobe.com/dc-acrobat-sdk-docs/pdfstandards/pdfreference1.7old.pdf#G9.1850134>`_
	and
	`Even-Odd Rule <https://opensource.adobe.com/dc-acrobat-sdk-docs/pdfstandards/pdfreference1.7old.pdf#G9.1850155>`_.

Line Cap Style

	PDFs define three different shapes for the ends of unclosed subpaths:
	butt cap, round cap, and square cap. See below for the visual effect and
	refer to the PDF specifications section about `Line Cap Styles
	<https://opensource.adobe.com/dc-acrobat-sdk-docs/pdfstandards/pdfreference1.7old.pdf#G9.1849678>`_
	for details.

	.. imagesvg:: ../../images/line-caps.svg
		:tagtype: object
		:width: 75%

Line Join Style

	PDFs define three different shapes for the joining of two lines in a
	subpath: miter join, round join, and bevel join. See below for the
	visual effects and refer to the PDF specifications section about `Line
	Join Styles <https://opensource.adobe.com/dc-acrobat-sdk-docs/pdfstandards/pdfreference1.7old.pdf#G9.1849699>`_
	for details.

	.. imagesvg:: ../../images/line-joins.svg
		:tagtype: object
		:width: 50%

Miter Limit

	When mitered line joins are used, then lines joining at sharper and
	sharper angles will produce longer and longer miters. The miter may stick
	out longer than anticipated. Therefore PDF defines a miter limit value,
	at which a longer miter join will be changed to a bevel join. See below
	for the visual effects and refer to the PDF specifications section about
	`Miter Limit
	<https://opensource.adobe.com/dc-acrobat-sdk-docs/pdfstandards/pdfreference1.7old.pdf#G9.3859627>`_
	for details.

	.. imagesvg:: ../../images/miter-limit.svg
		:tagtype: object
		:width: 75%

QuadPoint

	A QuadPoint in PDF is a non-axis aligned quadrilateral, used to define
	areas on the page that typically cover text (which may be rotated, or
	skewed). It is given as an array of 8 numbers (four x, y pairs).

	QuadPoints are used with Link and text markup annotations.

	The order of the points is a matter of confusion, because the order
	used in the PDF reference doesn't match the order that Adobe uses.

	This is the order that is typically used:
		``[ ulx uly urx ury llx lly lrx lry ]``

Page Box

	The PDF reference defines several boxes to determine different parts
	of a page. See the chapter on
	`Page Boundaries <https://opensource.adobe.com/dc-acrobat-sdk-docs/pdfstandards/pdfreference1.7old.pdf#G15.2260711>`_
	for more details.

	MediaBox
		The MediaBox defines the size of the physical medium on
		which the page is to be printed. It includes items that
		will be physically trimmed from the final product like
		crop marks, registration marks, etc.

	CropBox
		The CropBox defines the visible region of the page to
		be displayed or printed. This has no real meaning, but
		is used to clip the page contents when rendering.

	BleedBox
		The BleedBox defines the region to which the page
		contents expect to be clipped. This includes any extra
		bleed area to account for imprecision in the printing
		process.

	TrimBox
		The TrimBox defines the intended dimensions of the
		finished page after trimming.

	ArtBox
		The ArtBox defines the area where it is considered safe
		to place graphical elements.

Standard Structure Type

	The PDF specification defines how a PDF can specify a logical structure
	hierarchy of elements, similar to of HTML or XML. Each of the
	`defined structure elements <https://opensource.adobe.com/dc-acrobat-sdk-docs/pdfstandards/pdfreference1.7old.pdf#G15.2259688>`_,
	e.g. Div, BlockQuote, P, H1-H6 etc., are associated with some visual
	content.

Line Ending Style

	Styles used to draw line endings for certain annotations.
	Below is an illustration with the name of each style.
	The example uses black line color, with both none and
	blue interior color.

	.. imagesvg:: ../../images/line-ending-styles.svg
		:tagtype: object
		:width: 75%

Border Style

	Annotations have have two border styles:
		Solid, Dashed

	More fancy borders are defined by the :term:`border effect`.

Border Effect

	Fancier borders can be drawn with a border effect:
		None, Cloudy

Annotation Type

	There are many annotation types defined in the PDF reference.

	MuPDF supports the following types:
		Text, FreeText, Square, Circle, Line, Polygon,
		PolyLine, Highlight, Underline, Squiggly, StrikeOut,
		Redact, Stamp, Caret, Ink, Popup, FileAttachment,
		Redaction

	These types are not supported yet:
		Sound, Movie, RichMedia, Widget, Screen, PrinterMark,
		TrapNet, Watermark, 3D, Projection

Widget Type

	Widgets are a type of annotation.
	There are a few different subtypes:

	Btn
		Pushbutton, Check Boxes, Radio Buttons
	Tx
		Text Fields
	Ch
		Choice Fields (list box, combo box)
	Sig
		Signature Field

Icon Name

	Some annotations appear as an icon.
	The available icons differ per annotation type.

	Text
		Comment,
		Help,
		Insert,
		Key,
		NewParagraph,
		Note,
		Paragraph
	FileAttachment
		Graph,
		PaperClip,
		PushPin,
		Tag
	Sound
		Mic,
		Speaker
	Stamp
		Approved,
		AsIs,
		Confidential,
		Departmental,
		Draft,
		Experimental,
		Expired,
		Final,
		ForComment,
		ForPublicRelease,
		NotApproved,
		NotForPublicRelease,
		Sold,
		TopSecret

MIME-type

	A MIME-type is a string describing the type of data.
	PDF data has the MIME-type "application/pdf", while
	unknown data has the MIME-type
	"application/octet-stream". For further details see the
	specification that the PDF specification references:
	`RFC 2048 - Multipurpose Internet Mail Extensions
	(MIME) Part Two: Media Types
	<https://www.rfc-editor.org/info/rfc2048>`_.

Language code

	Language codes consists of a primary code, followed
	zero or more by subcodes each preceded by a hyphen,
	e.g. "en", "en-US", "kr", "zh-CN", "zh-TW".

	For further details see the PDF specification's section
	on `Language Identifiers
	<https://opensource.adobe.com/dc-acrobat-sdk-docs/pdfstandards/pdfreference1.7old.pdf#G15.2262093>`_.

Associated File

	TODO

CMYK JPEG

	The situation with JPEG and CMYK colorspaces is complicated, and depends on
	many factors such as App markers, the ColorTransform PDF parameter, and whether
	a JPEG is intended as a standalone or embedded in PDF.

	TODO: explain our behavior, and adobe's behavior, and when impossible situations appear