12.3.2 Inline Areas
Inline areas are areas that are parts of lines. An inline area has a position point that lies on one edge of its box and an orientation called the escapement direction, which is perpendicular to the edge of the box on which the position point lies. The point on the box which lies in the escapement direction from the position point and is on the opposite edge of the box is called the escapement point of the inline area.

NOTE 38

Informally the box has an arrow pointing from the position point that says place me so that the arrow lies parallel to the line I'm in.
Inline areas are positioned to form lines in the following manner. The writing-mode for a paragraph gives an inline-progression direction for the paragraph. There is a placement point associated with the process of constructing a line. The first inline area is oriented so that its escapement direction is the same as the inline-progression direction of the paragraph, and the point on the inline area's box opposite to the position point becomes the current placement point. The next area is placed so that its position point is coincident with the current placement point and oriented so that its escapement direction is the same as the inline-progression direction of the paragraph.  The point on the inline area's box opposite to the position point becomes the current placement point for placing the next area. This is illustrated in Figure 8, Inline Area Placement and Positioning.
The use of kerning modifies this positioning as illustrated in Figure 9, Positioning with Kerning.
The path containing the position points of the inline areas, which have the direction determined by the paragraph's writing-mode, is known as the placement path.  This is illustrated in Figure 10, Glyph Positioning for the Left-to-Right Writing-Mode for the left-to-right writing-mode and in Figure 11, Glyph Positioning for the Right-to-Left Writing-Mode for the right-to-left writing-mode.
There are additional steps in the process when the paragraph uses more than one writing-mode.  For example, in Figure 12, Mixed Writing-Mode for Hebrew and English, there is an inline-progression direction of left-to-right for the English text and an inline-progression direction of right-to-left for the Hebrew text.  In addition, line breaking becomes more complex in this case.
The alignment mode specified by the alignment mode property for the font resource also influences how glyphs are positioned, as illustrated in Figure 13, Scripts with Mixed Alignment Modes. There are characteristics on inlined flow objects that can modify this process.
An inline area also has a line-progression direction, which is perpendicular to the inline-progression direction for its paragraph. Certain characteristics of inline areas are specified in terms of the line-progression direction.