fix grammar errors

spec/modules/ROOT/pages/block-content-model.adoc

@@ -16,7 +16,7 @@ The following block elements belong to the basic content model by default:
 
 * paragraph
 * table cell
-* principle text of list item
+* principal text of list item
 
 Currently, the later two do not support block attributes.
 This is expected to change in a future revision of a specification so they behave more like a paragraph.

spec/modules/ROOT/pages/block-element.adoc

@@ -9,9 +9,9 @@ A block always starts at the beginning or effective beginning of a whole line an
 Block elements are separated from one another by boundaries.
 These boundaries are either implicit, such as an empty line, or explicit, such as a delimiter line that is part of an enclosure.
 An enclosure is a source characteristic of some blocks.
-Specifically, a block element consists of two or three source characteristic: an enclosure, content, and metadata.
+Specifically, a block element consists of two or three source characteristics: an enclosure, content, and metadata.
 Once parsed, the enclosure does not produce a block which is fundamentally different from a block without an enclosure.
-These three characteristic are described in the following sections.
+These three characteristics are described in the following sections.
 
 === Boundaries and enclosures
 

spec/outline.adoc

@@ -463,7 +463,7 @@ When set, a boolean attribute typically has an empty value.
 
 * A *block element*, referred to as a *block*, is a discrete, line-wise element in the document structure.
 * A block always starts and ends on a whole line (starts at beginning of a line or effective beginning and ends at the end of the same or different line.
-* A block may have two to three source characteristic: metadata, a body, and an enclosure.
+* A block may have two to three source characteristics: metadata, a body, and an enclosure.
 * Block structural forms include: paragraph, indented lines, delimited, macro, heading?, shorthand macro, list?, dlist? (lists and headings might also be referred to as prefixed?)
 ** May also need a "generated" form
 * The body of a block may have an enclosure that is formed by delimiter lines.