While the vowel is the core of the spoken syllable, the consonant is the base of most writing systems or rather of most phonograms in systems not totally segmental.
Diacritic marks in alphabetic writing systems change the segmental phoneme.
In more complex (e.g. syllabic) writing systems, diacritic marks may change either the onset, nucleus or coda or any combination thereof.
Diacritic marks may be added to the base without altering it, others may connect with it in easy ways and yet others may change the base glyph (but retain the base graph).
Logical diacritic marks are (systematic) graphic transformations of the base that are not glyph additions, e.g. rotation and mirroring.
True syllabograms are those that encompass all parts of a syllable, i.e. initial onset, medial nucleus and final coda, but since the boundaries (i.e. onset and coda) are optional, there are middle (nucleus), start (onset-nucleus), end (nucleus-coda) and full (onset-nucleus-coda) syllabograms.
Most syllabaries only feature one or two kinds of syllabograms and form other syllables by graphemic rules.
Writing systems can be categorized by the amount of graphs from the various categories in their repertoire. The contemporary English writing system, for instance, only uses first-level segmentals
Arbitrary or analytic syllabograms bear no shared characteristics among common neither onset, nucleus nor coda.
Synthetic syllabograms share graphic characteristics among common onset, nucleus or coda.
Systematic syllabograms share graphic characteristics among common onset, nucleus and coda.
Boundary, placeholder, space and punctuation are special kinds of glyphs / graphemes / characters that are present to quite different amounts in writing systems. They often can be considered forming a (supplementary) script of their own. Mathematic and other scientific symbols also constitute supplementary scripts that cannot become writing systems all by themselves.
analytic boundaries
[x]
e.g. hangul jamos, sinographic radicals
graphic boundaries
(x)
e.g. hangul blocks, sinographic blocks
first-level
free base sign
uppercase letter
second-level
bound base sign
lowercase letter
third-level
free diacritic mark
superscript uppercase letter
fourth-level
bound diacritic mark
superscript lowercase letter
(C)
first-level consonant
(V)
first-level vowel
(v)
second-level vowel
(c)
second-level consonant
(v)
diacritic vowel
(c)
diacritic consonant
(CV)
consonant with inherent vowel
(CV?)
consonant with inherent vowel, or none
(CV!)
consonant with inherent vowel, but not none
(CV)
consonant with canceled inherent vowel
(CX?)
consonant with any implied vowel, or none
(CX!)
consonant with any implied vowel, but not none
(CX=)
consonant with certain implied vowel
(C–)
consonant with canceled implied vowel
(C)
consonant with overruled implied vowel
(CCC)
consonant cluster with lexemically implied vowels at any positions (Egyptic hieroglyphs)
(CCC)
consonant cluster with lexemically implied vowels at certain positions