Implement default and required css 3 fonts features, fontFeatureSettings, sub-/super- script baseline-shift.

Activate OpenType localized forms and features required for proper display of composed characters and marks.

lib/props.js

@@ -260,6 +260,106 @@ const alignmentBaseline = PropTypes.oneOf(['baseline', 'text-bottom', 'alphabeti
 */
 const baselineShift = PropTypes.oneOfType([PropTypes.oneOf(['sub', 'super', 'baseline']), PropTypes.arrayOf(numberProp), PropTypes.string]);
 
+/*
+ 6.12. Low-level font feature settings control: the font-feature-settings property
+
+ Name:	font-feature-settings
+ Value:	normal | <feature-tag-value> #
+ Initial:	normal
+ Applies to:	all elements
+ Inherited:	yes
+ Percentages:	N/A
+ Media:	visual
+ Computed value:	as specified
+ Animatable:	no
+
+    This property provides low-level control over OpenType font features.
+
+    It is intended as a way of providing access to font features
+    that are not widely used but are needed for a particular use case.
+
+    Authors should generally use ‘font-variant’ and its related subproperties
+    whenever possible and only use this property for special cases where its use
+    is the only way of accessing a particular infrequently used font feature.
+
+    enable small caps and use second swash alternate
+    font-feature-settings: "smcp", "swsh" 2;
+    A value of ‘normal’ means that no change in glyph selection or positioning occurs due to this property.
+
+    Feature tag values have the following syntax:
+
+    <feature-tag-value> = <string> [ <integer> | on | off ]?
+    The <string> is a case-sensitive OpenType feature tag. As specified in the OpenType specification,
+    feature tags contain four ASCII characters.
+
+    Tag strings longer or shorter than four characters,
+    or containing characters outside the U+20–7E codepoint range are invalid.
+
+    Feature tags need only match a feature tag defined in the font,
+    so they are not limited to explicitly registered OpenType features.
+
+    Fonts defining custom feature tags should follow the tag name rules
+    defined in the OpenType specification [OPENTYPE-FEATURES].
+
+    Feature tags not present in the font are ignored;
+    a user agent must not attempt to synthesize fallback behavior based on these feature tags.
+
+    The one exception is that user agents may synthetically support the kern feature with fonts
+    that contain kerning data in the form of a ‘kern’ table but lack kern feature support in the ‘GPOS’ table.
+
+    In general, authors should use the ‘font-kerning’ property to explicitly enable or disable kerning
+    since this property always affects fonts with either type of kerning data.
+
+    If present, a value indicates an index used for glyph selection.
+
+    An <integer> value must be 0 or greater.
+
+    A value of 0 indicates that the feature is disabled.
+
+    For boolean features, a value of 1 enables the feature.
+
+    For non-boolean features, a value of 1 or greater enables the feature and indicates the feature selection index.
+
+    A value of ‘on’ is synonymous with 1 and ‘off’ is synonymous with 0.
+
+    If the value is omitted, a value of 1 is assumed.
+
+    font-feature-settings: "dlig" 1;       /* dlig=1 enable discretionary ligatures * /
+    font-feature-settings: "smcp" on;      /* smcp=1 enable small caps * /
+    font-feature-settings: 'c2sc';         /* c2sc=1 enable caps to small caps * /
+    font-feature-settings: "liga" off;     /* liga=0 no common ligatures * /
+    font-feature-settings: "tnum", 'hist'; /* tnum=1, hist=1 enable tabular numbers and historical forms * /
+    font-feature-settings: "tnum" "hist";  /* invalid, need a comma-delimited list * /
+    font-feature-settings: "silly" off;    /* invalid, tag too long * /
+    font-feature-settings: "PKRN";         /* PKRN=1 enable custom feature * /
+    font-feature-settings: dlig;           /* invalid, tag must be a string * /
+
+    When values greater than the range supported by the font are specified, the behavior is explicitly undefined.
+
+    For boolean features, in general these will enable the feature.
+
+    For non-boolean features, out of range values will in general be equivalent to a 0 value.
+
+    However, in both cases the exact behavior will depend upon the way the font is designed
+    (specifically, which type of lookup is used to define the feature).
+
+    Although specifically defined for OpenType feature tags,
+    feature tags for other modern font formats that support font features may be added in the future.
+
+    Where possible, features defined for other font formats
+    should attempt to follow the pattern of registered OpenType tags.
+
+    The Japanese text below will be rendered with half-width kana characters:
+
+    body { font-feature-settings: "hwid"; /* Half-width OpenType feature * / }
+
+    <p>毎日カレー食べてるのに、飽きない</p>
+
+    https://drafts.csswg.org/css-fonts-3/#propdef-font-feature-settings
+    https://developer.mozilla.org/en/docs/Web/CSS/font-feature-settings
+*/
+const fontFeatureSettings = PropTypes.string;
+
 const textSpecificProps = {
     ...pathProps,
     ...fontProps,
@@ -269,6 +369,7 @@ const textSpecificProps = {
     lengthAdjust,
     textLength,
     fontData: PropTypes.object,
+    fontFeatureSettings,
 };
 
 // https://svgwg.org/svg2-draft/text.html#TSpanAttributes