[mpeg-OTspec] Suggestion for minor correction on figure styles

[David Lemon]

As the culprit behind the current wording, I'll second Thomas' 
proposed clarifications (along with Valdimir's subsequent 
clarification). Back when I wrote this stuff, we held a strong 
assumption that the default figures would be lining in style and 
tabular in width. We still follow that practice, and recommend it as 
the safest default - but that's no reason for the spec to fail to 
allow for other approaches.

- thanks,
David Lemon
Sr Manager, Type Development
Adobe Systems, Inc.

408 536 4152
lemon at adobe.com


At 13:50 -0700 3/26/10, Thomas Phinney wrote:
>  >From a conversation between me and John Daggett of Mozilla, on a CSS
>mailing list. He wrote:
>
>>  OpenType spec just says "Users can switch between the lining and
>>  oldstyle sets by turning this feature on or off."
>>
>>  I think that may be a bug in the spec, if a designer uses old-style
>>  figures as the default glyphs for numerals then the statement above
>>  will be incorrect.
>
>He is of course correct. Further, the default figures in a typeface
>may be neither lining nor oldstyle, but in between or something else!
>To allow for default figures that are non-lining, or even neither
>lining nor oldstyle, I have made a more formal proposal out of my
>response.
>
>Currently the 'lnum' and 'onum' feature tags in 6.4.3.2 "Feature
>descriptions and implementations," include the following language
>(assuming they are the same as the current OT spec).
>
>LNUM
>
>Function: This feature changes selected figures from oldstyle to the
>default lining form.
>Example: The user invokes this feature in order to get lining figures,
>which fit better with all-capital text. Various characters designed to
>be used with figures may also be covered by this feature. In cases
>where lining figures are the default form, this feature would undo
>previous substitutions.
>Recommended implementation: The lnum table maps each oldstyle figure,
>and any associated characters to the corresponding lining form (GSUB
>lookup type 1).
>Application interface: For GIDs found in the lnum coverage table, the
>application passes a GID to the onum table and gets back a new GID.
>Even if the current figures resulted from an earlier substitution, it
>may not be correct to simply revert to the original GIDs, because of
>interaction with the figure width features, so it's best to use this
>table.
>UI suggestion: This feature should be inactive by default. Users can
>switch between the lining and oldstyle sets by turning this feature on
>or off. Note that this feature is distinct from the figure width
>features (pnum and tnum). When the user invokes this feature, the
>application may wish to inquire whether a change in width is also
>desired.
>
>
>ONUM
>
>Function: This feature changes selected figures from the default
>lining style to oldstyle form.
>Example: The user invokes this feature to get oldstyle figures, which
>fit better into the flow of normal upper- and lowercase text. Various
>characters designed to be used with figures may also have oldstyle
>versions.
>Recommended implementation: The onum table maps each lining figure,
>and any associated characters, to the corresponding oldstyle form
>(GSUB lookup type 1).
>Application interface: For GIDs found in the onum coverage table, the
>application passes a GID to the onum table and gets back a new GID.
>UI suggestion: Users can switch between the lining and oldstyle sets
>by turning this feature on or off. Note: This feature is separate from
>the figure-width features pnum and tnum. When the user changes figure
>style, the application may want to query whether a change in width is
>also desired.
>Script/language sensitivity: None.
>Feature interaction: This feature overrides the results of the Lining
>Figures feature (lnum).
>
>
>I hereby propose those sections of these two feature descriptions be
>replaced as follows. (Note that this also corrects a typo in the
>"lnum" application interface description, where onum was incorrectly
>referenced. Note also that there are parts both before and after the
>blocks I am amending, which can remain untouched.)
>
>
>LNUM
>
>Function: This feature changes selected non-lining figures to lining figures.
>Example: The user invokes this feature in order to get lining figures,
>which fit better with all-capital text. Various characters designed to
>be used with figures may also be covered by this feature. In cases
>where lining figures are the default form, this feature would undo
>previous substitutions.
>Recommended implementation: The lnum table maps each oldstyle figure,
>and any associated characters to the corresponding lining form (GSUB
>lookup type 1). If the default figures are non-lining, they too are
>mapped to the corresponding lining form.
>Application interface: For GIDs found in the lnum coverage table, the
>application passes a GID to the lnum table and gets back a new GID.
>Even if the current figures resulted from an earlier substitution, it
>may not be correct to simply revert to the original GIDs, because of
>interaction with the figure width features, so it's best to use this
>table.
>UI suggestion: This feature should be inactive by default. Users can
>switch between the default and lining figure sets by turning this
>feature on or off. Note that this feature is distinct from the figure
>width features (pnum and tnum). When the user invokes this feature,
>the application may wish to inquire whether a change in width is also
>desired.
>
>ONUM
>
>Function: This feature changes selected figures from the default or
>lining style to oldstyle form.
>Example: The user invokes this feature to get oldstyle figures, which
>fit better into the flow of normal upper- and lowercase text. Various
>characters designed to be used with figures may also have oldstyle
>versions.
>Recommended implementation: The onum table maps each lining figure,
>and any associated characters, to the corresponding oldstyle form
>(GSUB lookup type 1). If the default figures are non-lining, they too
>are mapped to the corresponding oldstyle form.
>Application interface: For GIDs found in the onum coverage table, the
>application passes a GID to the onum table and gets back a new GID.
>UI suggestion: Users can switch between the default and oldstyle
>figure sets by turning this feature on or off. Note: This feature is
>separate from the figure-width features pnum and tnum. When the user
>changes figure style, the application may want to query whether a
>change in width is also desired.
>
>
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