[css-floats] Start some notes on floats.

Author: tabatkins

css-floats/float-notes.md

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+Float Notes
+===========
+
+Three types of float: inline, side (block, inline), corner.
+Side and corner are "page floats".
+
+'float' is shorthand for:
+
+* float-origin: inline | block | flow-root | column | page | page( [ content-box | margin-box | bleed-box ] )
+	* 'float' defaults this to "inline" for left/right/start/end single keywords, to "block" for everything else.
+* float-policy: ??? (see Håkon's Figures draft)
+* float-position:
+	left | right | start | end |
+	block-start | block-end |
+	???
+* float-offset: [ <length> | <percentage> | <line-height-unit> ]{1,4}
+
+'clear' means "if something is already there (value of clear), I want to go somewhere else".
+
+* column, page - if you're not the first thing in this column/page + position, move to next fragment and try again
+
+Acceptable Floating Scenarios That Need Syntax
+----------------------------------------------
+
+1. inline left/right (today's float)
+2. side float to block side of current fragment
+	1. always float
+	2. float if close to edge, otherwise in-flow
+	3. float if crossing fragment boundary, otherwise in-flow
+		1. always up (same page, anchor pushes to next)
+		2. always down (next page, anchor left on previous)
+		3. use JLREQ 4.3.5 condition to determine up or down
+3. float to specific fragment
+	1. corner float
+	2. side float
+4. float to subsequent fragment
+	1. corner float
+	2. side float
+5. column spanning/intrusions?
+
+Auto-Switching Float Types
+--------------------------
+
+1. in-flow to side
+	1. become a side float if close to the edge (Figures’ snap() function)
+	2. become a side (bottom of current/top of next) float if falling across a fragment boundary
+1. inline/corner to side - some functionality to say if the leftover text space is too small, become a side float instead - JLREQ 4.3.3.e elaborates
+
+Syntaxes???
+-----------
+
+1: float: left | right
+
+2.1: float: block-start | block-end
+	* two block-end floats - first goes on bottom (similar to float: right)? Do we need a reverse keyword?
+
+2.2: float: snap && [ block-start <<length>>? || block-end <<length>>? || inline-start <<length>>? || inline-end <<length>>? ]
+
+2.3.1: float: before-break
+2.3.2: float: after-break
+2.3.3: float: across-break
+
+3/4. float: <position> && <origin>? && [ next ?? <integer> ]
+(Intentional that you have to specify a particular or subsequent fragment to use this grammar clause.)
+
+[Brad's thoughts on defining position](https://lists.w3.org/Archives/Public/www-style/2015Nov/0105.html)
+
+	3.1: float: top left 2;
+	3.2: float: block-start page 2; /* float to the top of the 2nd page */
+
+Allow %s for the fragment-locator?
+For long doc, allows to say "put this about halfway through",
+regardless of how it actually fragments on a given screen.
+Maybe just source-location + "next" is enough.
+
+Need to define what to do if there isn't a given fragment.
+
+
+Layout
+------
+
+The float-origin changes the float's CB.
+	* What happens if there's a BFC boundary between the float's anchor and the desired float-origin?
+		Floats shouldn't cross BFC boundaries.
+		Require reparenting?
+		Talk to implementors about this, as it'll be unpopular.
+
+Resolving conflicts: resolve floats outside-in?
+Start at page level, then work inward to find positions of things.
+
+Clearing
+--------
+
+Def need the 8 cardinal values matching float-position
+
+* 'both' for left+right
+* <origin> for all positions in that origin
+
+If you can't clear, then what?
+* stay in-flow (ignore 'float')
+* ignore 'clear', just float as normal.
+* disappear
+* move to another specified position
+
+float: top right;
+clear: top left / top right, top right / bottom right, bottom right / bottom left, bottom left / discard;
+clear: [ <clear-position> / <clear-behavior>? ]#
+* shift (default): shifts below stuff in clear-position (or above for bottom floats)
+* <position>
+* discard
+* unfloat
+* unclear
+* next <position>? / [ unfloat | unclear | discard ]? (default is unfloat) (triggers if there's no next fragment to go to)
+
+If you can clear, where to move to?
+* clear: left/right/both move you down
+* page/column floats move to next fragmentainer (or if they're a top float, maybe they want to move to bottom float)
+
+clear: top / bottom, bottom / next top;
+/* gives alternating top/bottom behavior, because we re-evaluate 'clear' when moving to another fragment */