Final answer:
The property that aligns text within its parent element is known as text alignment, which can be set using CSS for web content or formatting tools in text editors.
Step-by-step explanation:
The property that aligns text within its parent in the context of web design or document formatting is typically referred to as text alignment. This property can be set using CSS (Cascading Style Sheets) when dealing with web content or appropriate formatting settings in word processors and layout programs. The text alignment can be set to values such as left, right, center, or justify, which determines how the text is distributed within its containing element. In more advanced typographical settings, such as in the manuscript described, aspects like the ratio of the text-block and the derivation of line height from the alif character involve careful calculations related to the design principles used by calligraphers, ensuring that the text is aesthetically pleasing and well-proportioned to its surrounding space.