Donner supports inherited CSS text-indent as a signed absolute length, em, or percentage, with initial value 0. It accepts CSS-wide keywords and the normal cascade through stylesheets and inline styles. SVG2 does not define a text-indent presentation attribute.
The margin applies to the first formatted line of a <text> with a positive inline-size, including an explicit area with white-space:pre or nowrap. Percentages use that text area's own inline measure. em computes against the declaring element's unadjusted computed font-size before inheritance; a descendant's font-size or font-size-adjust does not reinterpret it. An inline <tspan> does not establish another indented block. Text without an inline-size area and text-on-path retain their existing flow.
The margin participates in first-line fitting, emergency wrapping and CSS tab stops. SVG relative positions apply afterward. A forced newline consumes the first line even when it is empty; an empty span does not. Later lines have no margin. Negative values enlarge the first line's available measure. A margin wider than the area still admits the first typographic unit. The margin is excluded from textLength content stretching.
This property preserves Donner's existing per-line pen-extent anchoring profile: an indent of I contributes I, I/2, or 0 to the first content position for start, middle, or end anchoring. This is a compatibility profile, not a claim of complete SVG2 content-area and line-box alignment. The existing base progression is left-to-right horizontally and top-to-bottom vertically. Backward-shaped runs retain their shaping; paragraph direction and bidi layout remain existing limitations. This feature adds no text-align extension.
The hanging and each-line flags, calculated values, and ex, ch, rem, and viewport units are rejected rather than accepted without effect. Other wrapping and text-path limitations are unchanged.
References: CSS Text 3 text-indent, SVG2 text layout, SVG2 inline-size.
1.15.0 