- From: Pierre-Anthony Lemieux <pal@sandflow.com>
- Date: Tue, 2 Feb 2016 21:58:55 -0800
- To: Glenn Adams <glenn@skynav.com>
- Cc: Dae Kim <dakim@netflix.com>, Nigel Megitt <nigel.megitt@bbc.co.uk>, TTWG <public-tt@w3.org>
Hi Glenn, > firstly, this question is well formed only with respect to inheritable properties; it doesn't apply to non-inheritable properties; Oh. I was thinking of using chained referential styling, i.e. define a style element with desired 'initial' values <style xml:id="s1" tts:color="white" tts:fontFamily="monospaceSerif"/> and reference the style in all other styles, e.g. <style xml:id="s2" style="s1" tts:color="yellow"/> Why would that not work? TTML1 states: "The use of chained referential styling encourages the grouping of style specifications into general and specific sets, which further aids in style specification reuse." > which effectively applies to all content that may be rendered in any region; however, this would not be a viable > strategy for an inheritable property that to both region and body, such as tts:visible: it is only viable for an inheritable > property that applies to body or a descendant of body and does not apply to region, e.g., tts:color; Ah. An inheritable property applies to descendants in the document structure, and would not apply to a region into which one of these descendants flows. Is that right? > tts:backgroundColor Why is backgroundColor not inheritable, whereas color is, BTW? I am pretty sure it was discussed 10 years ago, but I was not present :) Best, -- Pierre On Tue, Feb 2, 2016 at 8:26 PM, Glenn Adams <glenn@skynav.com> wrote: > > > On Tue, Feb 2, 2016 at 6:13 PM, Pierre-Anthony Lemieux <pal@sandflow.com> > wrote: >> >> Hi Glenn, >> >> Ok. What is the downside of using style inheritance to avoid having to >> set a property explicitly throughout the document, i.e. have all >> styles derive from a top-level style that overrides the initial >> values? > > > firstly, this question is well formed only with respect to inheritable > properties; it doesn't apply to non-inheritable properties; > > so, for an inheritable property, in TTML1, the only option is to specify the > property on the top-most inheritable element, namely, on region; so, e.g., > > <region tts:color='yellow'/> > > however, if there are multiple regions, one would be forced to specify this > on each region in turn; alternatively, one might specify: > > <body tts:color='yellow'>...</body> > > which effectively applies to all content that may be rendered in any region; > however, this would not be a viable strategy for an inheritable property > that to both region and body, such as tts:visible: it is only viable for an > inheritable property that applies to body or a descendant of body and does > not apply to region, e.g., tts:color; > > in contrast, in TTML2, again for inheritable properties only, we have the > option of either specifying the property on (1) the top-most inheritable > element, namely, on tt, or on (2) an initial element, which has the effect > of overriding the initial value applied to the top-most inheritable element; > > >> >> >> Best, >> >> -- Pierre >> >> On Tue, Feb 2, 2016 at 1:08 PM, Glenn Adams <glenn@skynav.com> wrote: >> > >> > >> > On Tue, Feb 2, 2016 at 1:27 PM, Pierre-Anthony Lemieux >> > <pal@sandflow.com> >> > wrote: >> >> >> >> Hi Glenn, >> >> >> >> Ok. What approach does XSL-FO and/or CSS take to allowing authors to >> >> avoid having to explicitly set a property through the document? >> > >> > >> > For non-inheritable properties, there is no mechanism other than direct >> > specification (XSL-FO) or a style rule or style attribute (CSS). Also, >> > initial values (for inheritable and non-inheritable properties) cannot >> > be >> > overridden in either XSL-FO or CSS, so defining an initial element for >> > this >> > purpose in TTML2 is effectively a new mechanism not found in either >> > XSL-FO >> > or CSS. >> > >> >> >> >> >> >> Thanks, >> >> >> >> -- Pierre >> >> >> >> On Tue, Feb 2, 2016 at 11:55 AM, Glenn Adams <glenn@skynav.com> wrote: >> >> > Because that is not how the semantics of styles in XSL-FO or CSS >> >> > work, >> >> > and >> >> > thus not how the semantics work in TTML (of any flavor). >> >> > >> >> > Specifying a non-inheritable property on an element to which that >> >> > property >> >> > does not apply is a NO-OP. >> >> > >> >> > In TTML1 we have the following (Section 8.2): >> >> > >> >> > Note: >> >> > >> >> > Due to the general syntax of this specification (and the schemas it >> >> > references) with respect to how style attributes are specified, >> >> > particularly >> >> > for the purpose of supporting inheritance, it is possible for an >> >> > author >> >> > to >> >> > inadvertently specify a non-inheritable style attribute on an element >> >> > that >> >> > applies neither to that element or any of its descendants while still >> >> > remaining conformant from a content validity perspective. Content >> >> > authors >> >> > may wish to make use of TTML content verification tools that detect >> >> > and >> >> > warn >> >> > about such usage. >> >> > >> >> > In TTML2 we promoted this to normative language (Section 10.2): >> >> > >> >> > Unless explicitly permitted by an element type definition, an >> >> > attribute >> >> > in >> >> > the TT Style Namespace should not be specified on an element unless >> >> > it >> >> > either applies to that element or denotes an inheritable style >> >> > property. >> >> > If >> >> > it does not apply to that element and does not denote an inheritable >> >> > style >> >> > property, then it must be ignored for the purpose of non-validation >> >> > processing. In the case of validation processing, such usage should >> >> > be >> >> > reported as a warning, or, if strict validation is performed, as an >> >> > error. >> >> > >> >> > >> >> > >> >> > >> >> > >> >> > On Tue, Feb 2, 2016 at 12:48 PM, Pierre-Anthony Lemieux >> >> > <pal@sandflow.com> >> >> > wrote: >> >> >> >> >> >> Hi Glenn, >> >> >> >> >> >> > tts:backgroundColor >> >> >> >> >> >> Can you remind us why specifying tts:backgroundColor="X" on <tt> >> >> >> could >> >> >> not mean "set initial value of tts:backgroundColor to X"? >> >> >> >> >> >> Best, >> >> >> >> >> >> -- Pierre >> >> >> >> >> >> On Tue, Feb 2, 2016 at 11:42 AM, Glenn Adams <glenn@skynav.com> >> >> >> wrote: >> >> >> > >> >> >> > >> >> >> > On Tue, Feb 2, 2016 at 12:28 PM, Pierre-Anthony Lemieux >> >> >> > <pal@sandflow.com> >> >> >> > wrote: >> >> >> >> >> >> >> >> Hi Glenn et al., >> >> >> >> >> >> >> >> >Perhaps we need to review >> >> >> >> > uninheritable properties in TTML2 to determine if we need to >> >> >> >> > upgrade >> >> >> >> > them to >> >> >> >> > inheritable, >> >> >> >> >> >> >> >> I like the idea of having a single mechanism for setting an >> >> >> >> initial >> >> >> >> value for properties, i.e. avoid having to set a property >> >> >> >> explicitly >> >> >> >> throughout the document. >> >> >> >> >> >> >> >> Expanding inheritance (instead of introducing a new <initial> >> >> >> >> element) >> >> >> >> seems promising, and intuitive. >> >> >> > >> >> >> > >> >> >> > That won't be sufficient, since we will not be able to make >> >> >> > everything >> >> >> > inherit. The reason for this is related to the semantics of >> >> >> > specific >> >> >> > style >> >> >> > properties. For example, the following cannot inherit: >> >> >> > >> >> >> > tts:backgroundColor >> >> >> > tts:backgroundImage >> >> >> > tts:backgroundPosition >> >> >> > tts:backgroundRepeat >> >> >> > tts:border >> >> >> > tts:bpd >> >> >> > tts:display >> >> >> > tts:extent >> >> >> > tts:ipd >> >> >> > tts:opacity >> >> >> > tts:origin >> >> >> > tts:overflow >> >> >> > tts:padding >> >> >> > tts:position >> >> >> > tts:ruby >> >> >> > tts:unicodeBidi >> >> >> > tts:writingMode >> >> >> > tts:zIndex >> >> >> > >> >> >> > Possible candidates for upgrading to inheritable are: >> >> >> > >> >> >> > tts:displayAlign >> >> >> > tts:showBackground >> >> >> > >> >> >> > So really, only these two are potentially able to be recast as >> >> >> > inheritable >> >> >> > in TTML2. All the rest (above) rely on initial value, and, for >> >> >> > that >> >> >> > matter, >> >> >> > initial value also applies to inheritable properties at the top of >> >> >> > the >> >> >> > inheritance tree (region in TTML1, tt in TTML2). >> >> >> > >> >> >> > The initial element is already written into the TTML2 spec, >> >> >> > implemented, >> >> >> > deployed, and previously discussed in the WG (though perhaps we >> >> >> > didn't >> >> >> > dive >> >> >> > in too deeply). >> >> >> > >> >> >> >> >> >> >> >> >> >> >> >> > though doing so will require careful consideration of >> >> >> >> > interoperability with TTML1 behavior. >> >> >> >> >> >> >> >> I see two scenarios: >> >> >> >> >> >> >> >> - an author wishes to create a document that conforms to both >> >> >> >> TTML1 >> >> >> >> and TTML2, in which case the author should set the property >> >> >> >> explicitly >> >> >> >> throughout the document -- this is always safe. >> >> >> >> >> >> >> >> - an author wishes to target only TTML2 processors, in which the >> >> >> >> author can rely on the expanded inheritance rules >> >> >> >> >> >> >> >> Are there other scenarios? >> >> >> >> >> >> >> >> Best, >> >> >> >> >> >> >> >> -- Pierre >> >> >> >> >> >> >> >> On Fri, Jan 29, 2016 at 9:33 AM, Glenn Adams <glenn@skynav.com> >> >> >> >> wrote: >> >> >> >> > >> >> >> >> > >> >> >> >> > On Fri, Jan 29, 2016 at 10:26 AM, Pierre-Anthony Lemieux >> >> >> >> > <pal@sandflow.com> >> >> >> >> > wrote: >> >> >> >> >> >> >> >> >> >> Hi Glenn, >> >> >> >> >> >> >> >> >> >> > This could also be done in other ways, such as by specifying >> >> >> >> >> > these >> >> >> >> >> > properties on the tt element, >> >> >> >> >> > from which all inheritance would occur (in TTML2); however, >> >> >> >> >> > that >> >> >> >> >> > wouldn't work for properties >> >> >> >> >> > that don't inherit, like tts:showBackground, etc. >> >> >> >> >> >> >> >> >> >> Why doesn't tts:showBackground inherit? >> >> >> >> > >> >> >> >> > >> >> >> >> > It was originally defined on region in TTML1, which has no way >> >> >> >> > for >> >> >> >> > a >> >> >> >> > region >> >> >> >> > to inherit. However, we are adding root element inheritance in >> >> >> >> > TTML2 >> >> >> >> > (e.g., >> >> >> >> > from tt to head to layout to region). Perhaps we need to review >> >> >> >> > uninheritable properties in TTML2 to determine if we need to >> >> >> >> > upgrade >> >> >> >> > them to >> >> >> >> > inheritable, though doing so will require careful consideration >> >> >> >> > of >> >> >> >> > interoperability with TTML1 behavior. >> >> >> >> > >> >> >> >> >> >> >> >> >> >> >> >> >> >> >> Thanks, >> >> >> >> >> >> >> >> >> >> -- Pierre >> >> >> >> >> >> >> >> >> >> On Fri, Jan 29, 2016 at 9:11 AM, Glenn Adams >> >> >> >> >> <glenn@skynav.com> >> >> >> >> >> wrote: >> >> >> >> >> > I can provide some respond to this. >> >> >> >> >> > >> >> >> >> >> > On Fri, Jan 29, 2016 at 8:14 AM, Pierre-Anthony Lemieux >> >> >> >> >> > <pal@sandflow.com> >> >> >> >> >> > wrote: >> >> >> >> >> >> >> >> >> >> >> >> Hi Dae, >> >> >> >> >> >> >> >> >> >> >> >> > initial >> >> >> >> >> >> >> >> >> >> >> >> How does Netflix plan to use <initial>? >> >> >> >> >> > >> >> >> >> >> > >> >> >> >> >> > The TTT tools already support the initial element with the >> >> >> >> >> > ttml2 >> >> >> >> >> > model, >> >> >> >> >> > and >> >> >> >> >> > has found it to be very useful in specifying a variety of >> >> >> >> >> > non-default, >> >> >> >> >> > global style settings, such as default color and font >> >> >> >> >> > related >> >> >> >> >> > properties, >> >> >> >> >> > etc. >> >> >> >> >> > >> >> >> >> >> > For example, the CAP2TT tool in TTT specifies a test >> >> >> >> >> > configuration >> >> >> >> >> > file >> >> >> >> >> > that >> >> >> >> >> > specifies a template for generating TTML2 output files in >> >> >> >> >> > which >> >> >> >> >> > is >> >> >> >> >> > specified >> >> >> >> >> > the following: >> >> >> >> >> > >> >> >> >> >> > <initial tts:fontSize="4vh"/> >> >> >> >> >> > <initial tts:lineHeight="5vh"/> >> >> >> >> >> > <initial tts:showBackground="whenActive"/> >> >> >> >> >> > >> >> >> >> >> > Here, initial is used to alter the default initial value. >> >> >> >> >> > This >> >> >> >> >> > could >> >> >> >> >> > also be >> >> >> >> >> > done in other ways, such as by specifying these properties >> >> >> >> >> > on >> >> >> >> >> > the >> >> >> >> >> > tt >> >> >> >> >> > element, from which all inheritance would occur (in TTML2); >> >> >> >> >> > however, >> >> >> >> >> > that >> >> >> >> >> > wouldn't work for properties that don't inherit, like >> >> >> >> >> > tts:showBackground, >> >> >> >> >> > etc. >> >> >> >> >> > >> >> >> >> >> > Note that be using initial to specify an explicit >> >> >> >> >> > tts:lineHeight, >> >> >> >> >> > then >> >> >> >> >> > there >> >> >> >> >> > is no possibility of using the default initial value of >> >> >> >> >> > 'normal' >> >> >> >> >> > (which >> >> >> >> >> > has >> >> >> >> >> > been a problem with IMSC content). >> >> >> >> >> > >> >> >> >> >> > It is also useful for redefining the default initial value >> >> >> >> >> > of >> >> >> >> >> > tts:backgroundColor and resolving the platform dependent >> >> >> >> >> > default >> >> >> >> >> > initial >> >> >> >> >> > value of tts:color. >> >> >> >> >> > >> >> >> >> >> > >> >> >> >> >> >> >> >> >> >> >> >> >> >> >> > >> >> >> > >> >> > >> >> > >> > >> > > >
Received on Wednesday, 3 February 2016 05:59:46 UTC